Eighth Edition

Estelle Levetin The University of Tulsa Karen McMahon The University of Tulsa

lev80044_fm_i-xvi.indd 1 2/26/19 11:53 AM PLANTS & SOCIETY, EIGHTH EDITION

Published by McGraw- Hill Education, 2 Penn Plaza, New York, NY 10121. Copyright © 2020 by McGraw-Hill Education. All rights reserved. Printed in the United States of America. Previous editions © 2016, 2012, and 2008. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of McGraw-Hill Education, including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning.

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ISBN 978-1-259-88004-9 (bound edition) MHID 1-259-88004-4 (bound edition) ISBN 978-1-260-81260-2 (loose-leaf edition) MHID 1-260-81260-X (loose-leaf edition)

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Library of Congress Cataloging-in- Publication Data

Names: Levetin, Estelle, author. | McMahon, Karen, editor. Title: Plants & society / Estelle Levetin, The University of Tulsa, Karen McMahon, The University of Tulsa. Other titles: Plants and society Description: Eighth edition. | New York, NY : McGraw-Hill Education, [2020] | Includes index. Identifiers: LCCN 2019001477| ISBN 9781259880049 (alk. paper) | ISBN 9781260812602 (loose-leaf edition) Subjects: LCSH: Botany. | Botany, Economic. | Plants—Social aspects. Classification: LCC QK47 .L48 2020 | DDC 580—dc23 LC record available at https://lccn.loc.gov/2019001477

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lev80044_fm_i-xvi.indd 2 2/26/19 11:53 AM In loving memory of our mothers

Pauline Levetin & Dorothy Sink McMahon

lev80044_fm_i-xvi.indd 3 2/26/19 11:53 AM Contents in Brief

UNIT I Plants and Society: The Botanical Connections to Our Lives 1 Plants in Our Lives 1

UNIT II Introduction to Plant Life: Botanical Principles 2 The Plant Cell 16 3 The Plant Body 28 4 Plant Physiology 47 5 Plant Life Cycle: Flowers 69 6 Plant Life Cycle: Fruits and Seeds 85 7 Genetics 101 8 Plant Systematics and Evolution 120 9 Diversity of Plant Life 136

UNIT III Plants as a Source of Food 10 Human Nutrition 152 11 Origins of Agriculture 175 12 The Grasses 187 13 Legumes 210 14 Starchy Staples 224 15 Feeding a Hungry World 241

UNIT IV Commercial Products Derived from Plants 16 Stimulating Beverages 271 17 Herbs and Spices 289 18 Materials: Cloth, Wood, and Paper 308

UNIT V Plants and Human Health 19 Medicinal Plants 337 20 Psychoactive Plants 358 21 Poisonous and Allergy Plants 378

UNIT VI Algae and Fungi: The Impact of Algae and Fungi on Human Affairs 22 The Algae 400 23 Fungi in the Natural Environment 419 24 Beverages and Foods from Fungi 446 25 Fungi That Affect Human Health 469

UNIT VII Plants and the Environment 26 Plant Ecology 486

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Preface xii 3 The Plant Body 28 List of Boxed Readings xv Plant Tissues 29 Meristems 29 UNIT I Plants and Society: Dermal Tissue 29 The Botanical Connections Ground Tissue 31 to Our Lives Vascular Tissue 32 Plant Organs 33 Stems 33 1 Plants in Our Lives 1 Roots 35 Plants and Human Society 2 Leaves 37 The Flowering Plants 2 A CLOSER LOOK 3.1 Studying Ancient Tree Rings 37 The Non- Flowering Plants 4 The Algae 4 Vegetables: Edible Plant Organs 41 The Fungi 4 Carrots 41 Plant Sciences 4 A CLOSER LOOK 3.2 Plants That Trap Animals 42 Scientific Method 5 Lettuce 44 A CLOSER LOOK 1.1 Biological Mimics 6 Radishes 44 Fundamental Properties of Life 6 A CLOSER LOOK 3.3 Supermarket Botany 44 Molecules of Life 8 Asparagus 45 Carbohydrates 8 Proteins 9 Lipids 11 4 Plant Physiology 47 Nucleic Acids 12 Plant Transport Systems 48 A CLOSER LOOK 1.2 Perfumes to Poisons: Plants as Transpiration 49 Chemical Factories 14 Absorption of Water from the Soil 49 A CLOSER LOOK 4.1 Mineral Nutrition and the Green Clean 50 UNIT II Introduction to Plant Life: Water Movement in Plants 51 Botanical Principles Translocation of Sugar 51 2 The Plant Cell 16 A CLOSER LOOK 4.2 Sugar and Slavery 53 Metabolism 55 Early Studies of Cells 17 Energy 55 The Cell Wall 19 Redox Reactions 55 The Protoplast 19 Phosphorylation 55 Membranes 19 Enzymes 56 Moving Into and Out of Cells 19 Photosynthesis 56 Organelles 20 Energy from the Sun 56 A CLOSER LOOK 2.1 Origin of Chloroplasts Chloroplasts and Light- Absorbing Pigments 57 and Mitochondria 22 Overview 59 The Nucleus 23 The Light Reactions 59 Cell Division 24 The Calvin Cycle 61 The Cell Cycle 24 Variation to Carbon Fixation 63 Prophase 24 Cellular Respiration 63 Metaphase 25 Glycolysis 64 Anaphase 27 The Krebs Cycle 64 Telophase 27 The Electron Transport System 64 Cytokinesis 27 Aerobic vs. Anaerobic Respiration 67

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5 Plant Life Cycle: Molecular Genetics 110 Flowers 69 DNA— The Genetic Material 111 A CLOSER LOOK 7.2 Try These Genes On for Size 112 The Flower 70 Floral Organs 70 Genes Control Proteins 114 Transcription and the Genetic Code 114 A CLOSER LOOK 5.1 Mad about Tulips 71 Translation 116 Modified Flowers 72 Other Roles of RNA 116 Meiosis 75 Mutations 117 Stages of Meiosis 75 Epigenetics 118 Meiosis in Flowering Plants 77 Recombinant DNA 118 Male Gametophyte Development 77 A CLOSER LOOK 5.2 Pollen Is More Than Something 8 Plant Systematics to Sneeze At 79 and Evolution 120 Female Gametophyte Development 79 Early History of Classification 121 Pollination and Fertilization 79 Carolus Linnaeus 121 Animal Pollination 80 How Plants Are Named 123 A CLOSER LOOK 5.3 Alluring Scents 82 Common Names 123 Wind Pollination 83 A CLOSER LOOK 8.1 The Language of Flowers 125 Double Fertilization 83 Scientific Names 126 Taxonomic Hierarchy 127 6 Plant Life Cycle: Higher Taxa 127 Fruits and Seeds 85 What Is a Species? 129 Fruit Types 86 Phylocode 130 Simple Fleshy Fruits 86 A CLOSER LOOK 8.2 Saving Species through Dry Dehiscent Fruits 86 Systematics 131 Dry Indehiscent Fruits 86 Barcoding Species 132 Aggregate and Multiple Fruits 86 The Influence of Darwin’s Theory of Seed Structure and Germination 88 Evolution 132 Dicot Seeds 88 The Voyage of the HMS Beagle 133 Monocot Seeds 88 Natural Selection 134 Seed Germination and Development 88 Representative Edible Fruits 88 9 Diversity of Plant Life 136 Tomatoes 90 The Three- Domain System 137 A CLOSER LOOK 6.1 The Influence of Hormones Survey of the Plant Kingdom 137 on Plant Reproductive Cycles 92 A CLOSER LOOK 9.1 Alternation of Apples 94 Generations 139 Oranges and Grapefruits 95 Chestnuts 97 Liverworts, Mosses, and Exotic Fruits 98 Hornworts 141 Lycophytes and Ferns 143 7 Genetics 101 Gymnosperms 146 A CLOSER LOOK 9.2 Amber: A Glimpse Mendelian Genetics 102 into the Past 148 Gregor Mendel and the Garden Pea 102 Angiosperms 151 Monohybrid Cross 103 Dihybrid Cross 105 UNIT III Plants as a Source of Food Beyond Mendelian Genetics 106 Incomplete Dominance 106 10 Human Nutrition 152 A CLOSER LOOK 7.1 Solving Genetics Macronutrients 153 Problems 107 Sugars and Complex Multiple Alleles 109 Carbohydrates 153 Polygenic Inheritance 109 A CLOSER LOOK 10.1 Famine or Linkage 109 Feast 154

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Fiber in the Diet 156 Corn Genome 199 Proteins and Essential Amino Acids 156 Value of Corn 199 Gluten and Celiac Disease 158 Rice: Food for Billions 200 Fats and Cholesterol 159 A Plant for Flooded Fields 200 Micronutrients 162 Varieties 201 Vitamins 162 Rice Genome 202 Minerals 167 Flood-­Tolerant Rice 202 Dietary Guidelines 169 Other Important Grains 202 Balancing Nutritional Requirements 169 Rye and Triticale 202 Healthier Dietary Guidelines 170 Oats 204 Glycemic Index 171 Barley and Tritordeum 204 Meatless Alternatives 172 Sorghum and Millets 204 A CLOSER LOOK 10.2 Eat Broccoli for Cancer Other Grasses 205 Prevention 172 Forage Grasses 205 Lawn Grasses 205 11 Origins of Bioethanol: Grass to Gas 206 Corn 206 Agriculture 175 Sugarcane 207 Foraging Societies and Their Cellulosic Ethanol 207 Diets 176 Early Foragers 176 Modern Foragers 177 13 Legumes 210 The Paleo Diet 177 Characteristics of the Legume A CLOSER LOOK 11.1 Forensic Botany 178 Family 211 Agriculture: Revolution or A CLOSER LOOK 13.1 The Nitrogen Evolution? 179 Cycle 212 Latitudinal Spread 180 Important Legume Food Crops 214 Early Sites of Agriculture 180 Beans and Peas 214 The Near East 181 Peanuts 215 The Far East 182 Soybeans 217 The New World 183 A CLOSER LOOK 13.2 Harvesting Oil 219 Characteristics of Domesticated Other Legumes of Interest 221 Plants 184 A Supertree for Forestry 221 Centers of Plant Domestication 184 Forage Crops 221 Beans of the Future 222 12 The Grasses 187 Characteristics of the Grass 14 Starchy Staples 224 Family 188 Storage Organs 225 Vegetative Characteristics 188 Modified Stems 225 The Flower 188 Storage Roots 226 The Grain 188 A CLOSER LOOK 14.1 Banana Republics: Wheat: The Staff of Life 189 The Story of the Starchy Fruit 226 Origin and Evolution of Wheat 190 Modern Cultivars 191 White Potato 228 Wheat Genome 191 South American Origins 228 A CLOSER LOOK 12.1 The Rise of Bread 192 The Irish Famine 228 Continental Europe 229 Nutrition 193 The Potato in the United States 229 Corn: Indian Maize 193 Solanum tuberosum 230 An Unusual Cereal 194 Pathogens and Pests 231 Types of Corn 194 Potato Genome 232 A CLOSER LOOK 12.2 Barbara McClintock Modern Cultivars 232 and Jumping Genes in Corn 196 Sweet Potato 232 Hybrid Corn 197 Origin and Spread 233 Ancestry of Corn 197 Cultivation 233

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Cassava 234 Regulatory Issues 266 Origin and Spread 234 Environmental and Safety Considerations 266 Botany and Cultivation 234 Gene Editing: CRISPR/Cas9 268 Processing 235 A CLOSER LOOK 14.2 Starch: In Our Collars UNIT IV Commercial Products and in Our Colas 237 Derived from Plants Other Underground Crops 238 Yams 238 16 Stimulating Beverages 271 Taro 238 Physiological Effects of Jerusalem Artichoke 238 Caffeine 272 Medical Benefits of Caffeine 273 15 Feeding a Hungry Coffee 273 World 241 An Arabian Drink 273 Plantations, Cultivation, Breeding for Crop and Processing 274 Improvement 242 A CLOSER LOOK 16.1 Climate Change and the The Green Revolution 243 Future of Coffee 276 High-Yield­ Varieties 243 Disease-Resistant­ Varieties 244 From Bean to Brew 277 History of the Green Revolution 245 Varieties 277 Problems with the Green Revolution: What Went Decaffeination 278 Wrong? 245 Variations on a Bean 279 Solutions? 246 Shade Coffee vs. Sun Coffee 279 Genetic Diversity 247 Fair Trade Coffee 279 Monoculture 247 Tea 279 Sustainable Agriculture 248 Oriental Origins 279 Genetic Erosion 249 Cultivation and Processing 280 Seed Banks 249 A CLOSER LOOK 16.2 Tea Time: Ceremonies Heirloom Varieties 250 and Customs around the World 280 Germplasm Treaty 250 The Flavor and Health Effects of Tea 281 Crops and Global Warming 251 History 282 Alternative Crops: The Search for Chocolate 283 New Foods 252 Food of the Gods 283 Quinoa 252 Quakers and Cocoa 283 Amaranth and Chia 252 A CLOSER LOOK 16.3 Candy Bars: Tarwi 253 For the Love of Chocolate 284 Tamarillo and Naranjilla 254 Cultivation and Processing 285 Oca 254 The High Price of Chocolate 286 Biotechnology 254 Coca- Cola: An “All- American” Drink 287 A CLOSER LOOK 15.1 Mutiny on the HMS Bounty: Other Caffeine Beverages 287 The Story of Breadfruit 255 Cell and Tissue Culture 256 17 Herbs and Spices 289 Molecular Plant Breeding 257 Essential Oils 290 Genetic Engineering and Transgenic History of Spices 290 Plants 257 Ancient Trade 290 Herbicide Resistance 258 Against the Grain 260 A CLOSER LOOK 17.1 Aromatherapy: Insect Resistance 260 The Healing Power of Scents 291 Bt Corn and Controversy 261 Marco Polo 291 The Promise of Golden Rice 262 Age of Exploration 292 Other Genetically Engineered Foods 262 Imperialism 293 Disease Resistance 263 New World Discoveries 293 Farming Pharmaceuticals 264 Spices 293 Nonfood Crops 265 Cinnamon: The Fragrant Bark 293 Genetically Modified Trees 265 Black and White Pepper 294

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Cloves 295 Medicinal Plants 343 Nutmeg and Mace 295 Foxglove and the Control of Heart Disease 343 Ginger and Turmeric 296 Aspirin: From Willow Bark to Bayer 345 Saffron 297 Malaria, the Fever Bark Tree, and Sweet Hot Chilies and Other Capsicum Peppers 297 Wormwood 346 Vanilla 299 Diabetes, French Lilac, and Metformin 349 Allspice 300 Snakeroot, Schizophrenia, and Hypertension 350 Herbs 300 The Burn Plant 351 The Aromatic Mint 301 Ephedrine 351 The Parsley Family 303 Cancer Therapy 352 The Mustard Family 303 Herbal Remedies: Promise and Problems 354 The Pungent Alliums 304 A CLOSER LOOK 17.2 Sweet Talk 306 20 Psychoactive Plants 358 Psychoactive Drugs 359 18 Materials: Cloth, Wood, The Opium Poppy 360 and Paper 308 An Ancient Curse 360 Fibers 309 The Opium Wars 360 Types 309 Opium Alkaloids 361 Heroin 361 A CLOSER LOOK 18.1 A Tisket, a Tasket: Withdrawal 362 There Are Many Types of Baskets 310 Marijuana 362 King Cotton 312 Early History in China and India 362 Linen: An Ancient Fabric 315 Spread to the West 363 Other Bast Fibers 316 THC and Its Psychoactive Effects 364 Miscellaneous Fibers 317 Medical Marijuana 365 Rayon: “Artificial Silk” 319 Legal Issues 365 Bark Cloth 319 Cocaine 366 A CLOSER LOOK 18.2 Herbs to Dye For 321 South American Origins 366 Wood and Wood Products 323 Freud, Holmes, and Coca- Cola 366 A CLOSER LOOK 18.3 Good Vibrations 324 A CLOSER LOOK 20.1 The Tropane Alkaloids and Witchcraft 367 Hardwoods and Softwoods 326 Lumber, Veneer, and Plywood 327 Coke and Crack 369 Fuel 329 Medical Uses 369 Other Products from Trees 329 A Deadly Drug 369 Wood Pulp 330 Tobacco 370 Paper 331 A New World Habit 370 Early Writing Surfaces 331 Cultivation Practices 371 The Art of Papermaking 333 Health Risks 371 Alternatives to Wood Pulp 333 Peyote 374 Bamboo 334 Mescal Buttons 374 Native American Church 375 UNIT V Plants and Human Health Kava— The Drug of Choice in the Pacific 375 Preparation of the Beverage 375 19 Medicinal Plants 337 Active Components in Kava 375 Lesser Known Psychoactive Plants 376 History of Plants in Medicine 338 Early Greeks and Romans 338 Age of Herbals 338 21 Poisonous and Allergy A CLOSER LOOK 19.1 Native American Plants 378 Medicine 340 Notable Poisonous Plants 379 Modern Prescription Drugs 340 Poisonous Plants in the Wild 379 Herbal Medicine Today 342 Poisonous Plants in the Active Principles in Plants 343 Backyard 382 Alkaloids 343 A CLOSER LOOK 21.1 Allelopathy—Chemical­ Glycosides 343 Warfare in Plants 383

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Poisonous Plants in the Home 386 A CLOSER LOOK 23.1 Lichens: Algal-Fungal­ Plants Poisonous to Livestock 386 Partnership 434 Plants That Cause Mechanical Injury 387 Mycorrhizae: Root- Fungus Partnership 435 Insecticides from Plants 388 A CLOSER LOOK 23.2 Dry Rot and Other Wood Allergy Plants 389 Decay Fungi 436 Allergy and the Immune System 390 Respiratory Allergies 390 Plant Diseases with Major Impact Hay Fever Plants 391 on Humans 437 Climate Change and Allergy Plants 394 Late Blight of Potato 438 Allergy Control 394 Rusts— Threat to the World’s Contact Dermatitis 395 Breadbasket 439 Food Allergies 397 Corn Smut— Blight or Delight 441 Latex Allergy 398 Dutch Elm Disease— Destruction in the Urban Landscape 441 Sudden Oak Death— Destruction in the UNIT VI Algae and Fungi: The Impact of Forest 443 Algae and Fungi on Human Affairs 24 Beverages and Foods 22 The Algae 400 from Fungi 446 Characteristics of the Algae 401 Making Wine 447 Classification of the Algae 401 The Wine Grape 448 Cyanobacteria 402 Harvest 449 Euglenoids 403 Red or White 449 Dinoflagellates 403 Fermentation 449 Diatoms 404 A CLOSER LOOK 24.1 Disaster in the Brown Algae 404 French Vineyards 450 Red Algae 405 Clarification 452 Green Algae 405 Aging and Bottling 452 Algae in Our Diet 409 “Drinking Stars” 453 Seaweeds 409 Fortified and Dessert Wines 454 Biofuels from Algae 410 Climate Change and the Wine Grape 454 Other Economic Uses of Algae 411 The Brewing of Beer 454 Toxic and Harmful Algae 411 Barley Malt 455 Toxic Cyanobacteria 412 Mash, Hops, and Wort 455 A CLOSER LOOK 22.1 Drugs from the Sea 413 Fermentation and Lagering 455 Red Tides 414 Sake, a Rice “Beer” 457 Pfiesteria 414 Distillation 457 A CLOSER LOOK 22.2 Killer Alga— Story of a Deadly The Still 458 Invader 415 Distilled Spirits 458 The Whiskey Rebellion 458 Other Toxic Algae 417 Tequila from Agave 459 Hard Cider 460 23 Fungi in the Natural A Victorian Drink Revisited 461 Environment 419 Absinthe 461 Fungi and Fungal- Like The Green Hour 461 Organisms 420 Active Principles 461 Fungal-Like­ Protists 420 Absinthism 462 Slime Molds 421 A CLOSER LOOK 24.2 Alcohol and The Kingdom Fungi 422 Health 463 Characteristics of Fungi 422 Fungi as Food 465 Classification of Fungi 424 Edible Mushrooms 465 Role of Fungi in the Environment 433 Fermented Foods 466 Decomposers—Nature’s­ Recyclers 433 Quorn Mycoprotein 467

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25 Fungi That Affect Human Biogeochemical Cycling 492 The Carbon Cycle 492 Health 469 Source or Sink? 492 Antibiotics and Other Wonder The Greenhouse Effect 494 Drugs 470 Species Shift 496 Fleming’s Discovery of Penicillin 470 Global Warming Pact 496 Manufacture of Penicillin 471 Ecological Succession 497 Other Antibiotics and Antifungals 471 The Anthropocene Epoch 498 Fungal Poisons and Toxins 472 The Green World: Biomes 500 Mycotoxins 472 Deserts 501 A CLOSER LOOK 25.1 The New Wonder Drugs 473 Crops from the Desert 501 Ergot of Rye and Ergotism 475 Chaparral 504 The Destroying Angel and Toadstools 477 Grasslands 504 Soma and Hallucinogenic Fungi 478 Forests 505 Human Pathogens and Allergies 480 Harvesting Trees 506 Dermatophytes 480 A CLOSER LOOK 26.1 Buying Time for the Rain Systemic Mycoses 481 Forest 508 Allergies 482 Indoor Fungi and Toxic Molds 482 Appendix A Atoms, Molecules, and Chemical UNIT VII Plants and the Bonds 513 Environment Appendix B Classification of Plants and Those Organisms Traditionally Classified 26 Plant Ecology 486 as Plants Discussed in Plants and Society 517 The Ecosystem 487 Ecological Niche 487 Appendix C Metric System: Scientific Food Chains and Food Webs 488 Measurement 519 Energy Flow and Ecological Glossary 521 Pyramids 489 Index 533 Biological Magnification 491

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n the twenty- first century, plant science is once again assuming a prominent role in research. Renewed empha- ORGANIZATION sis on developing medicinal products from native plants I We feel that Plants and Society is a textbook with a great deal has encouraged ethnobotanical endeavors. The destruction of of flexibility for course design. It offers a unique balanced the rain forests has made the timing for this research impera- approach between basic botany and the applied or economic tive and has spurred efforts to catalog the plant biodiversity in aspects of plant science. Other texts emphasize either the these environments. Efforts to feed the growing populations in basic or applied material, making it difficult for instructors developing nations have also positioned plant scientists at the who wish to provide better balance in an introductory course. cutting edge of genetic engineering with the creation of trans- Another distinctive feature is the unit on algae and fungi. genic crops. However, in recent decades botany courses have While other texts cover certain aspects of this topic, we have seen a decline in enrollment, and some courses have even dis- an expanded coverage of algae and fungi and their impact on appeared from the curriculum in many universities. We have society. written Plants and Society in an effort to offset this trend. By Plants and Society is organized into 26 chapters that are taking a multidisciplinary approach to studying the relation- grouped into seven units. The first nine chapters cover the ship between plants and people, we hope to stimulate inter- basic botany found in an introductory course. However, even est in plant science and encourage students to further study. in these chapters we have included many applied topics, some Also, by exposing students to society’s historical connection to in the boxed essays but others directly in the chapter text. plants, we hope to instill a greater appreciation for the botan- ical world. UNIT I Plants and Society: The Botanical Connections to Our Lives. Chapter 1 stresses the overall importance of plants in everyday life. The properties of life, molecules of life, AUDIENCE flowering and non flowering plants, algae, and fungi are introduced. The scientific method is explained as the pro- Recently, general botany courses have emphasized the impact cess used by scientists to study and expand our knowledge of plants on society. In addition, many institutions have of the natural world. The diversity and applications of developed plants and society courses devoted exclusively to phytochemicals are also presented. this topic. This emphasis has transformed the traditional economic botany from a dry statistical treatment of “bushels UNIT II Introduction to Plant Life: Botanical Principles. This per acre” to an exciting discussion of “botanical marvels” that unit addresses basic botany. Chapters cover plant struc- have influenced our past and will change our future. Plants ture from the cellular level to the mature plant. Repro- and Society is intended for use in this type of course, which duction, including mitosis and meiosis and the life cycle is usually one semester or one quarter in length. There are of flowering plants, is discussed in two chapters. Other no prerequisites because it is an introductory course. The chapters cover genetics, evolution, plant physiology, plant course covers basic principles of botany and places a strong systematics, and plant diversity. Some of the economic emphasis on the economic aspects and social implications of aspects of plants discussed in this unit are the importance plants and fungi. of vegetables and fruits, the connection between sugar Students usually take a course of this nature in their fresh- and slavery, plant essential oils and perfumes, phytore- man or sophomore year to satisfy a science requirement in the mediation, the applications of palynology, and species general education curriculum. Typically, they are not biology conservation. majors. Although most students enroll to satisfy the science UNIT III Plants as a Source of Food. This unit describes the requirement, many become enthusiastic about the subject mat- major food crops. It begins with a chapter on the require- ter. Students, even those with a limited science background, ments for human nutrition and continues with a chapter should not encounter any problems with the level of scientific on the origins of agriculture. Other chapters cover the detail in this text. grasses, the legumes, and starchy staples. The unit ends As indicated, the primary market for this text is a plants with a chapter on the Green Revolution, the loss of and society course; however, it would certainly be suitable for genetic diversity, the search for alternative crops, and the an introductory general botany course as well. controversial development of transgenic crops.

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UNIT IV Commercial Products Derived from Plants. This unit their knowledge to real-life situations. Thinking Critically covers other crops that provide us with consumable prod- questions may also be assigned by instructors or used to ini- ucts, such as beverages, herbs and spices, and materials tiate in-class discussions. Three appendices and a glossary such as cloth, wood, and paper. The historical origin and conclude the text. The classification of plants and other societal impact of these crops are explored. organisms discussed in the text and a review of metric units UNIT V Plants and Human Health. This unit introduces stu- are located for quick access on the inside front and back dents to the historical foundations of Western medicine, covers, respectively. the practice of herbal medicine, and the chemistry of sec- ondary plant products. Descriptions of the plants that pro- vide us with medicinal products and psychoactive drugs NEW TO THE EIGHTH EDITION are discussed. The unit also covers the common poisonous The eighth edition of Plants and Society been updated to spot- and allergy plants that are found in the environment. light exciting discoveries and update major advancements in UNIT VI Algae and Fungi: The Impact of Algae and Fungi the science of plants, algae, and fungi, with special emphasis on Human Affairs. This unit describes the economic on how these organisms impact humanity. These include: importance of the algae and fungi, including their biol- ogy and crucial roles in the environment. The algae are • Expanded information on the regulation of cell division recognized as key producers in aquatic environments (Chapter 2) and as sources of human food, devastating blooms, and • Subsidiary cells in grasses enable the greater inflation industrial products. Fermented beverages and foods from of guard cells to bring in more carbon dioxide for fungi are discussed, as is the medical importance of fungi photosynthesis as well as facilitating guard cells to as sources of antibiotics, toxins, and diseases affecting respond rapidly to changing environmental conditions crops and people. (Chapter 3). • Sun pitchers (Heliamphora), carnivorous pitcher plants UNIT VII Plants and the Environment. Chapter 26 is an native to South America, exhibit remarkable adaptations: introduction to the principles of ecology: the ecosystem, a nectar spoon to lure prey and a drainage pipe to niches, food chains, biogeochemical cycles, and ecological siphon off excess water from the pitcher (Chapter 3). succession. The major biomes of the world are discussed, • The section on orchids has been updated to include with an emphasis on the economic value of certain desert significantly more detail on the unique modifications of plants and the strategy of extractive reserves in the rain orchid flowers (Chapter 5). forest. The problems associated with rising levels of the • There are updates on the latest research surrounding greenhouse gas CO2 and the environmental consequences colony collapse disorder and the search for alternative of global warming are addressed. pollinators (Chapter 5). • There is additional coverage of the ways in which researchers are using genomic analysis to discover how APPROACH to enhance the flavors of mass- market tomatoes to better This textbook is written at the introductory level suitable for resemble heirloom varieties (Chapter 6). students with little or no background in biology. Like any • Information on CRISPR, a powerful technique in the introductory book, this book uses a broad-brush treatment. gene editing of organisms, is presented (Chapters 7 The nature of the course dictates an applied approach, with and 15). Fiber in the diet may promote health as the food to support the impact of plants on society as the integrating theme, but • microbiota beneficial to the digestive tract (Chapter 10). the theoretical aspects of basic botany are thoroughly covered. • The paleo diet, the so- called original diet of ancient humans, is evaluated (Chapter 11). • A new update on the International Wheat Genome LEARNING AIDS Sequencing Consortium’s work to sequence the bread In addition to the textual material, each chapter begins with wheat genome is featured (Chapter 12). a chapter outline and key concepts. Important terms are in • A Closer Look 13.1 has been updated to include new boldface type throughout the text, and each chapter ends information on biofertilizers and A Closer Look 13.2 on with a summary and review questions. Thinking Critically Harvesting Oil also has data updates (Chapter 13). questions are inserted in the text to draw the attention • A Closer Look 14.1 features new information on the of the students as they read the chapter. The questions recent resurgence of Panama disease and its effect on begin with either a summary of the preceding text or an bananas (Chapter 14). introduction to new information that is complementary • New evidence on the disjunct distribution of sweet to the chapter. The questions that follow are designed not potatoes is detailed (Chapter 14). only to test comprehension but also, in many instances, • A section on the effects of global warming on crops has to promote critical thinking by asking students to apply been included (Chapter 15).

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• Information on genetically modified rice and corn has been added (Chapter 15). ACKNOWLEDGMENTS • A new Closer Look on Climate Change and the Future From our first introduction to botany as college students, of Coffee has been added (Chapter 16). we became irrevocably fixated on the lives of plants. We can • Update on the legal status of hemp cultivation remember the fascination we felt when we read about the plant (Chapter 18). explorers who discovered extinct ginkgo trees alive in China • There is a new content on the increased use of plant and how a trichome of the stinging nettle was the inspiration biomass (such as wood pellets) to supplement or replace for the invention of the hypodermic needle. It is our hope that coal (Chapter 18). Plants and Society will present the world of plants and how • A new section highlights the remarkable history of they sustain humanity in a way that will inspire students to French lilac in the development of the medicine have a lifelong appreciation of plants. Metformin, which is used to treat both diabetes and We wish to thank the editorial staff at McGraw-Hill Higher polycystic ovarian syndrome (Chapter 19). Education for their editorial expertise and their endless • Updated content is included on the antimalarial patience during the publication of the eighth edition of Plants properties of certain plants used in Chinese medicine and Society. We especially want to acknowledge our Portfolio (Chapter 19). Manager, Michael Ivanov; Senior Product Developer, Chipper • Updates on the legal status of marijuana has been Scheid; Freelance Product Developer, Jen Thomas; and Con- included (Chapter 20). tent Project Manager, Becca Gill. • Giant Hogweed, an oversized invasive weed from Asia, produces a toxic sap that causes debilitating blisters and burns to the skin upon exposure to sunlight (Chapter 21). • There are updates to gluten and nonceliac gluten REVIEWERS sensitivity (Chapter 21). We are indebted to our colleagues who have taken time • There is information on new research suggesting from demanding schedules to meticulously review Plants and a potential connection between algae blooms and global Society for errors, inconsistencies, or omissions and to offer warming (Chapter 22). constructive feedback and suggestions. We thank you for mak- • A 2018 research on Batrachochytrium dendrobatidis ing the eighth edition of Plants and Society the best edition. fungus highlights how the pathogen traveled from the Korean peninsula and has been responsible for the Karen Amisi extinction or decline of frog and salamander populations Grand Valley State University around the world (Chapter 23). Elise C. Hollister • A new section covers the history and cultivation of apple Grand Valley State University ciders, the alcoholic beverages made by fermenting apple Meshagae Hunte-Brown­ juice (Chapter 24). Drexel University • With the rise of MRSA infections worldwide, there has Arthur Kneeland been renewed interest in the therapeutic use of fusidic University of Wisconsin— Stout acid, covered now in additional detail (Chapter 25). Diane M. Lahaise • The global, indelible impact of human activity on Earth Georgia State University— Perimeter College has initiated a demand for the creation of a new geologic Elizabeth Martin epoch, the Anthropocene (Chapter 26). Lewis- Clark State College • The Paris Climate Agreement has revised its long- term Michael Sundue goal of limiting global warming from an increase of University of Vermont 2.0°C above preindustrial temperatures down to 1.5°C Jacob Thompson (Chapter 26). College of Coastal Georgia • Over 50 new photographs and several new or revised Alexander Wait figures and tables have been added to the eighth edition. Missouri State University

lev80044_fm_i-xvi.indd 14 2/26/19 11:54 AM List of Boxed Readings

1. Biological Mimics (Chapter 1) 25. Harvesting Oil (Chapter 13) 2. Perfumes to Poisons: Plants as Chemical Factories 26. Banana Republics: The Story of the Starchy Fruit (Chapter 1) (Chapter 14) 3. Origin of Chloroplasts and Mitochondria (Chapter 2) 27. Starch: In Our Collars and in Our Colas (Chapter 14) 4. Studying Ancient Tree Rings (Chapter 3) 28. Mutiny on the HMS Bounty: The Story of Breadfruit 5. Plants That Trap Animals (Chapter 3) (Chapter 15) 6. Supermarket Botany (Chapter 3) 29. Climate Change and the Future of Coffee (Chapter 16) 7. Mineral Nutrition and the Green Clean (Chapter 4) 30. Tea Time: Ceremonies and Customs around the World 8. Sugar and Slavery (Chapter 4) (Chapter 16) 9. Mad about Tulips (Chapter 5) 31. Candy Bars: For the Love of Chocolate (Chapter 16) 10. Pollen Is More Than Something to Sneeze At 32. Aromatherapy: The Healing Power of Scents (Chapter 5) (Chapter 17) 11. Alluring Scents (Chapter 5) 33. Sweet Talk (Chapter 17) 12. The Influence of Hormones on Plant Reproductive 34. A Tisket, a Tasket: There Are Many Types of Baskets Cycles (Chapter 6) (Chapter 18) 13. Solving Genetics Problems (Chapter 7) 35. Herbs to Dye For (Chapter 18) 14. Try These Genes On for Size (Chapter 7) 36. Good Vibrations (Chapter 18) 15. The Language of Flowers (Chapter 8) 37. Native American Medicine (Chapter 19) 16. Saving Species through Systematics (Chapter 8) 38. The Tropane Alkaloids and Witchcraft (Chapter 20) 17. Alternation of Generations (Chapter 9) 39. Allelopathy— Chemical Warfare in Plants (Chapter 21) 18. Amber: A Glimpse into the Past (Chapter 9) 40. Drugs from the Sea (Chapter 22) 19. Famine or Feast (Chapter 10) 41. Killer Alga—Story of a Deadly Invader (Chapter 22) 20. Eat Broccoli for Cancer Prevention (Chapter 10) 42. Lichens: Algal- Fungal Partnership (Chapter 23) 21. Forensic Botany (Chapter 11) 43. Dry Rot and Other Wood Decay Fungi (Chapter 23) 22. The Rise of Bread (Chapter 12) 44. Disaster in the French Vineyards (Chapter 24) 23. Barbara McClintock and Jumping Genes in Corn 45. Alcohol and Health (Chapter 24) (Chapter 12) 46. The New Wonder Drugs (Chapter 25) 24. The Nitrogen Cycle (Chapter 13) 47. Buying Time for the Rain Forest (Chapter 26)

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course information. Order a Create book, and you’ll receive PLANTS AND SOCIETY COMPANION a complimentary print review copy in 3–5 business days or WEBSITE a complimentary electronic review copy (eComp) via email in minutes. Go to www.mcgrawhillcreate.com today and register The companion website to accompany Plants and Society to experience how McGraw-Hill Create TM empowers you to offers a variety of additional resources for instructors and stu- teach your students your way. dents. Instructors will appreciate full- color PowerPoint image slides that contain illustrations and photos from the text, along with suggested activities. A comprehensive bank of test ques- tions, aligned with each chapter of the text, is also available THE LABORATORY MANUAL FOR along with access to TestGen. TestGen. allows instructors to APPLIED BOTANY BY LEVETIN, create paper and online tests or quizzes in one easy- to-use pro- gram. Students will find multiple-choice quizzes, short-answer MCMAHON, AND REINSVOLD concepts, and further resources to aid in their study. Also The lab manual features 18 exer- included is a listing of useful and poisonous plants, as well as cises that focus on examining tips for growing houseplants and home gardening. plants and plant products that www.mhhe.com/levetin8e have sustained or affected human society. Although the manual includes standard information on Craft your teaching plant cells and tissues, there is a resources to match practical approach to the inves- the way you teach! tigations. Students extract plant With McGraw-Hill­ dyes, make paper from plant CreateTM, www.mcgrawhillcreate.com, you can easily rear- fibers, and study starch grains range chapters, combine material from other content sources, used in archeology. Several labo- and quickly upload content you have written like your course ratory topics are devoted exclusively to economically import- syllabus or teaching notes. Find the content you need in ant crops— grasses, legumes, starchy staples, and spices. Four Create by searching through thousands of leading McGraw- additional appendixes—titled Science as a Process, A Field Hill textbooks. Arrange your book to fit your teaching style. Trip to a Health Food Store, A Taster’s Sampler of Caffeine Create even allows you to personalize your book’s appearance Beverages and Foods, and Notes for Instructors— provide addi- by selecting the cover and adding your name, school, and tional information for each of the labs.

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lev80044_fm_i-xvi.indd 16 2/26/19 11:54 AM UNIT III

CHAPTER 10 Human Nutrition

Nutrition Facts label imparts important nutritional information for the consumer.

KEY CONCEPTS 1. Human nutritional needs are supplied by macronutrients (carbohydrates, proteins, and fats) and micronutrients (vitamins and minerals). 2. If nutritional requirements are not satisfied, deficiency diseases can result that have widespread effects on the bodily systems. 3. Plants can supply the majority of human nutritional requirements, and there is evidence that increasing the proportion of plant foods in the diet can have positive health benefits.

©Karen McMahon CHAPTER OUTLINE Dietary Guidelines 169 Balancing Nutritional Requirements 169 Macronutrients 153 Healthier Dietary Guidelines 170 Sugars and Complex Carbohydrates 153 Glycemic Index 171 A CLOSER LOOK 10.1 Famine A CLOSER LOOK 10.2 Eat Broccoli or Feast 154 for Cancer Prevention 172 Fiber in the Diet 156 Meatless Alternatives 172 Proteins and Essential Amino Acids 156 Chapter Summary 173 Gluten and Celiac Disease 158 Fats and Cholesterol 159 Review Questions 174 Micronutrients 162 Vitamins 162 Minerals 167

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ew ideas in nutrition are quickly incorporated by the Monosaccharides health-conscious segment of society and advertisers Monosaccharides are the basic building blocks of all carbo- N looking for a new marketing gimmick. The benefits of hydrates, and glucose is the most abundant of these sugars. several nutritional concepts, such as fiber, monounsaturated During the process of digestion, many carbohydrates are bro- oils, and low-carbohydrate diets, have made headlines and influ- ken down or converted into glucose, which is then transported enced lifestyle changes. All these concepts promise better health by the blood to all the cells in the body. Within cells, the and many are, in fact, dependent on a greater consumption of process of cellular respiration metabolizes glucose to produce plants in the human diet. This chapter will examine human the energy necessary to sustain life. Other common mono- nutritional needs and how plants can satisfy these needs. saccharides are fructose and galactose, which have the same chemical makeup as glucose, C6H12O6, differing only in the arrangement of the atoms within the molecules. In the body, MACRONUTRIENTS most of the fructose and galactose is converted into glucose The basic nutritional needs of humans are to supply energy and metabolized as such. In the United States, an inexpensive and raw materials for all the various activities and processes sweetener for many types of processed foods is high-fructose that occur in the body. In addition to the need for water, corn syrup, often preferred because fructose is sweeter-tasting humans require five types of nutrients from their food sup- than table sugar. Fructose is commonly found in many fruits, ply; three of these are required in relatively large amounts unlike galactose, which does not normally occur free in nature. and are called macronutrients, consisting of carbohydrates, proteins, and fats. The other two types of nutrients, vitamins Disaccharides and minerals, are required in small amounts and are known Disaccharides are composed of two monosaccharides chemi- as micronutrients. If water were removed, the macronutrients cally joined together. The most common disaccharide is sucrose, would make up almost all the dry weight of foods.* or table sugar, formed from a molecule of glucose and a molecule Human energy requirements vary with the age, sex, and of fructose. Other disaccharides are the milk sugar lactose (a activity level of the individual, within a wide range of 1,200 to combination of glucose and galactose) and maltose (formed by 3,200 kilocalories per day. The current recommendation for two glucose molecules), which are largely found in germinating Americans is an average daily intake of 2,000 kilocalories or grains. Table sugar, which primarily comes from sugarcane and 1,600 kilocalories for women and 2,200 kilocalories for men. sugar beet, is at least 97% pure sucrose with little nutritional value, (A calorie is a measure of energy—technically, the amount of thereby supplying only kilocalories. (See A Closer Look 4.2: energy needed to raise the temperature of 1 gram of water Sugar and Slavery.) During digestion, these disaccharides are by 1 degree Celsius.) Food energy is normally measured in broken down to yield their component monosaccharides. kilocalories (1,000 calories = 1 kilocalorie), which can be abbre- viated as kcal, or Calories with a capital C. Most dietary guides Polysaccharides simply use the term calories, but this book will use the more Polysaccharides, also known as complex carbohydrates, con- accurate Calories or kilocalories. Each gram of c arbohydrate tain hundreds to thousands of individual sugar units, and for or protein can supply 4 kilocalories; for each gram of fat con- the most part, glucose is the only monosaccharide present. sumed, the amount of energy supplied is more than double, The different polysaccharides are distinguished by the way in 9 kilocalories. Although all the macronutrients can be used as which the glucose units are joined together, their arrangement, a source of energy, normally only carbohydrates and fats do so, and their number. Starch is the storage form of glucose found while proteins provide the raw materials, or building blocks, in plants; it occurs abundantly in seeds, some fruits, tubers, required for the synthesis of essential metabolites, growth, and and taproots. The presence of starch in foods can be traced tissue maintenance. The consequences of undernutrition, mal- directly to its plant origin; the starch in white bread and pasta nutrition, and overnutrition for the world’s population are the was originally stored in the grain of a wheat plant. The major topics of A Closer Look 10.1: Famine or Feast. grain crops (wheat, rice, and corn), the major underground crops (potato, sweet potato, and cassava), and the major Sugars and Complex Carbohydrates legumes (beans and peas) supply the majority of starch in the Although carbohydrates are commonly grouped into sugars human diet. In the body, starch is broken down into glucose and starches, recall (see Chapter 1) that these compounds can by enzymes in saliva and the small intestine and is transported be chemically classified into monosaccharides, disaccharides, by the bloodstream to body cells. and polysaccharides, based on the number of sugar units in Glycogen is the body’s storage form of glucose, found in the molecule. the liver and skeletal muscles. When the levels of glucose in the blood are higher than the demands of the cells, the excess *All organisms have nutrient needs requiring some compounds in large amounts (mac- is used for the synthesis of glycogen in liver and muscle cells. ronutrients) and other compounds in smaller amounts (micronutrients). The elements Only a limited amount of glycogen can be stored as a reserve— that plants require, macronutrients and micronutrients refer to the mineral require- ments. When referring to human nutritional needs, these terms take on a different no more than a day’s worth of energy needs. Excess glucose meaning, as discussed here. beyond this amount is generally converted to fat. During

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In 2018, estimates of the world population size were The counterpart to the conditions of undernutrition and placed at 7.7 billion, with a projection of 9.8 billion by malnutrition is overnutrition, in which an excessive intake the year 2050 (box fig. 10.1a). This unprecedented popu- of food can result in obesity and chronic disease. Currently, lation growth presents many problems related to the pro- a global epidemic of obesity is the chief concern of many duction and distribution of sufficient food to meet human public health officials. nutritional needs. Although global food production has increased during recent decades, chronic hunger and mal- nutrition are ever-present problems in many developing 10 nations, especially in sub-Saharan Africa and Asia. It is 9 estimated that 815 billion people suffer from undernutri- 8 tion. In addition, many are malnourished and deficient in vitamin A, iron, iodine, or zinc. Undernutrition is defined 7 as an insufficient number of kilocalories to maintain daily 6 energy requirements, while malnutrition is a quality defi- ciency in which one or more essential nutrients is lacking, 5 even though caloric intake may be sufficient. The majority 4 of starvation-related deaths are among children, with about (billions) Population half of those dying under the age of five. Starvation is usu- 3 ally the underlying cause of death, but most die of diseases 2 such as diarrhea or measles, which would not be fatal in a 1 properly nourished individual. Two devastating conditions specifically related to under- 6000 5000 4000 3000 2000 1000 B.C. A.D. 1000 2018 nourishment and malnourishment are kwashiorkor and (a) marasmus (box figs. 10.1b and c). Kwashiorkor occurs when the diet is deficient in protein but has sufficient kilocalories. It is particularly prevalent after weaning, when a child no longer receives the protein-rich breast milk and is switched to a starchy diet low in protein content or quality or both. Symptoms of kwashiorkor include puffy skin and swollen belly due to edema, a fatty liver, a reddish orange and Pr cast to the ionentverol hair, dermatitis, and listlessness. Marasmus results from starvation when the diet is low in both kilocalo-

ries and protein; other nutrients are C ontse probably deficient as well. Sufferers from marasmus are extremely thin and

shriveled—literally, skin and CceourS bones fent: as or Diseaer the muscles of the body, even the heart muscle, are wasted away because muscle protein is digested to supply energy needs. The overt symptoms of Conrad/CDC Lyle Source: Dr. both marasmus and kwashiorkor can (b) (c) be reversed if treated in time, but espe- Box Figure 10.1 (a) The human population has continued to grow rapidly, up to cially in infants and young children, mild 7.3 billion in 2015, as indicated by the J-shaped curve. (b) A child suffering from mental retardation and stunted growth kwashiorkor, a protein-deficiency disease. (c) Marasmus victims have a skeletal appearance may be permanent results. as the body wastes from starvation.

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lev80044_ch10_152-174.indd 154 2/19/19 11:54 AM The WHO (World Health Organization), which first listed The repercussions of childhood obesity can be devas- obesity as a disease in 1979, has asked the UN member tating. As with adult obesity, childhood obesity is linked to nations to adopt programs in their home countries to reduce numerous complications: hypertension, sleep apnea, asthma, the intake of foods high in fats and sugar. It is ironic that negative self-image, and gallstones, among others. Type 2 developed nations, which have nearly eradicated many diabetes, formerly rare in adolescence, is now on the rise in nutritional deficiencies, are now faced with a new nutri- children, mainly as a consequence of childhood obesity. In tional threat with the prevalence of overweight and obesity. some populations, 50% of the newly diagnosed are adoles- Developing nations are also experiencing a rise in obesity in cents. In January 2004, the American Academy of Pediatrics certain populations—often at a faster rate than that seen in issued the statement that “overweight is the most common industrialized nations—at the same time that they are trying medical condition of childhood.” to combat the serious problem of undernutrition. The global epidemic of obesity appears to be directly Almost 40% of U.S. adults (20–74 years) in 2015–2016 related to an energy imbalance. In most cases, obesity is were overweight or obese, up from 14% in 1971. This increase caused by an excessive consumption of energy-rich foods, has been seen for both men and women and across all eth- especially those high in sugar and/or saturated fats, coupled nic, socioeconomic, and age groups. The United States is with inadequate expenditure of energy due to the limited not alone; obesity has been identified as a growing health physical activity associated with a modern, urban lifestyle. In problem in the United Kingdom, Australasia, Eastern Europe, the United States, some researchers suggest that the prev- the Middle East, and the Pacific Islands—all these areas have alence of fast foods in the American diet should take much seen the incidence of obesity more than triple since 1980. of the blame for the fattening of Americans. Others have The WHO estimates that globally more than 1.9 billion adults advocated a sin tax on sugary snack foods and soft drinks to are overweight, with 650 million of them obese. Estimates discourage their consumption. of obesity vary widely, from below 5% of the population in Responding to the nation’s rising obesity rate, the Surgeon China and Japan and some African nations to greater than General released The Surgeon General’s Call to Action to 75% in urban Samoa. Prevent and Decrease Overweight and Obesity in 2001. Body mass index (BMI) is the most current method health The report warns that health problems resulting from the care professionals and fitness experts use to determine if a current epidemic of obesity could reverse many of the health person’s weight poses a health risk. BMI calculates a per- gains achieved in the United States in recent decades. It son’s body weight in kilograms per square meter (BMI = details specific steps to educate the American people about body wt in kg/[ht in m]2 or body wt in lb/[ht in in.]2 × 703). obesity-linked health issues and what actions should be taken Most people are considered overweight if their BMI ranges to reduce the incidence of obesity in the American popula- from 25 up to 30. A BMI of 30 or more indicates obesity; tion. Released in 2002, Healthier U.S. Initiative is encourag- a rating of 40 or greater is indicative of severe obesity. An ing Americans to prevent obesity by being physically active optimal BMI for most adults is below 25, and a BMI below every day and making healthier choices in their diets. 18.5 is considered underweight. The average BMI for adults Critics have countered that the so-called obesity epidemic in Africa and Asia ranges from 22 to 23, while a range of 25 was exaggerated by flawed statistical studies and the media. to 27 is the norm in North America, Europe, and some Latin The research behind the obesity epidemic headlines was American, North African, and Pacific Island nations. heavily funded by the weight-loss industry, which may have Obesity is associated with a higher risk of many diseases influenced the results. Newer studies report that there is only and chronic conditions: type 2 diabetes, hypertension (high a small increase in mortality rates of the mildly obese and, blood pressure), cardiovascular disease, stroke, asthma, in fact, the underweight, even when smokers are excluded, gallstones, cancers (prostate, breast, and colon), and osteo- have a higher death rate when compared with those of nor- arthritis. Eighty percent of obese adults suffer from one mal weight. Critics note that the researchers who identified of these diseases; 40% have two or more. Recently, it has obesity as a major cause of death in the United States did been shown that women who are overweight in their 70s not consider the impact of recent medical advancements, have a higher risk of developing Alzheimer’s disease in their which have significantly improved the outlook for people late 80s. with heart disease, diabetes, and high blood pressure, dis- The alarming rise in childhood obesity over the past two eases associated with obesity. Another observation ignored decades has been documented in many countries: Haiti, is that obesity can have a protective effect in the elderly. Costa Rica, Chile, Brazil, England, Scotland, China, Egypt, Elderly patients who are mildly obese usually outlive their Australia, Ghana, Morocco, and others. In 2015–2016, 18.5% normal-weight cohorts when hospitalized for an extended of children and adolescents (ages 2–19) in the United States time. Apparently, a nutritional reserve can be helpful in the are classified as overweight or obese). In the world, it is esti- recovery process. Colon cancer and postmenopausal breast mated that 41 million children under the age of 5 were over- cancer are slightly elevated in the obese, but lung cancer weight or obese. Developing countries have a 30% higher rates are surprisingly lower. The effects of obesity on health rate of increase in childhood overweight and obesity levels are probably more complex than once thought, and further than that of developed nations. research is needed.

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strenuous exercise, the body’s glycogen reserves are called husk from the seed coat of several species of plantain upon; therefore, athletes training for a competition practice a (Plantago ovata, Plantago arenaria) is an especially valuable regimen of carbohydrate loading by eating lots of starchy foods dietary fiber because it is a good source of both soluble and to build up muscle glycogen reserves. insoluble fiber. A study, which tracked the diets of more than 700,000 Fiber in the Diet people for over 20 years, found that those eating the least amount of fiber (less than 10 grams per day) were at an Another important dietary component is which is fiber, increased risk of colorectal cancer. The study also suggested derived from plant sources. Although not digestible, it does that fiber from cereals and whole grains, but not fruits and provide bulk and other benefits. There are many types of vegetables, is best for slightly lowering the risk of rectal dietary fiber: cellulose, lignin, hemicellulose, pectin, gums, cancer. Physicians and nutritionists still advocate the value mucilages, and others. Cellulose, a principal component of of fiber in lowering the risk of obesity, heart disease, and plant cell walls, is another polysaccharide composed of glu- diabetes. cose; however, humans do not have the enzymatic ability to The value of fiber in the diet in promoting health has break the bonds connecting the glucose molecules in cellulose been widely reported, but the exact mechanism by which a as they do for starch and glycogen, and thus cellulose passes high-fiber diet brings about these benefits has been unknown through the digestive tract as roughage, largely unaltered. until recently. Studies indicate that fiber plays a critical role Other cell wall components considered dietary fiber are lignin, in maintaining a healthy microbiota in the gut. Humans have pectins, and hemicelluloses. Lignin, a cell-wall component in a limited number of enzymes in the digestive tract and cannot plant cells that have secondary walls, is not a polysaccharide make the enzymes needed to breakdown dietary fiber, but but a complex polymer. Pectins and hemicelluloses, which are certain bacteria in the microbiota that inhabits the human cell wall polysaccharides, form the matrix in which cellulose intestines can. In other words, dietary fiber is the food or fuel fibrils are embedded. Pectins also occur in the middle lamella for these bacteria, and if a diet is high in dietary fiber, the between adjacent cells. Gums and mucilages are exudates population of these bacteria rises and health benefits accom- from various plants that are used commercially as thickening pany this rise. For example, when the bacteria digest fiber, agents in prepared foods. Cell wall polysaccharides, refined they often produce short-chain fatty acids as waste, which are from some species of red and brown algae, can also be consid- in turn then consumed by the intestinal cells as an important ered dietary fiber. Although not digestible by human enzymes, source of fuel. some fiber, especially some hemicelluloses, can be broken Experiments in which mice were switched from feeding down by intestinal bacteria and the nutrients made available on a high-fiber diet to a fiber-free, high fat, and high pro- to the body. tein diet show that the microbiota in their guts underwent

Dietary fiber can be conveniently grouped into two types, rapid changes in species composition. Some populations of and relating to their solubility in water. soluble insoluble, the microbiota crashed or disappeared completely; on the Insoluble fiber includes cellulose, lignin, and some hemicel- other hand, the bacterial species that fed on protein and fat luloses, while soluble fiber includes other hemicelluloses, increased significantly. Deprived of fiber for fuel, some bacte-

pectins, gums, mucilages, and the algal polysaccharides. rial species start to feed on the mucus layer of the intestines.

Soluble fiber is resistant to digestion and absorption in the Mucus is the layer lining the gut produced by intestinal cells

small intestine, but as soluble fiber enters the large intestine, it that coats the intestinal lining and protects intestinal cells is acted upon by naturally occurring bacteria. The bacteria fer- from digestive enzymes and invasive bacteria. If intestinal ment soluble fiber into gases and products beneficial to health. cells are deprived of the short-chained fatty acids provided by Butyric acid is one of these products. It is known to stabilize fiber-eating bacteria, the health of the intestinal cells declines blood glucose levels, which decreases the risk of type 2 diabe- and the result is a thinner mucus layer. With a thinner mucus tes. Butyric acid also has been shown to reduce blood levels of layer, bacteria can begin to penetrate the intestinal wall trig- cholesterol, reducing the risk of cardiovascular disease, and to gering the body’s immune response to destroy the invaders. raise the acidity of the colon, which prevents cancerous polyps The end result is chronic inflammation and may result in (small, tumorlike growths on the lining of the large intestine) conditions such as ulcerative colitis, a painful chronic bowel from forming. disease. Fruits, vegetables, seeds, and whole grains supply most of the fiber in the human diet. Some plants are higher in one or more of these types of fiber, and the beneficial effects of Proteins and Essential Amino Acids high fiber foods differ depending on which fiber is abundant. Proteins are a group of large, complex molecules that serve as For example, the soluble fiber present as gum in oat bran structural components and regulate a large variety of bodily and as pectin in apples is believed to lower cholesterol levels functions (table 10.1). Recall that the constituents of proteins in the blood. Wheat bran, which is largely cellulose, an insol- are amino acids; there are 20 naturally occurring amino acids, uble fiber, has no particular cholesterol-lowering ability but which can be assembled in various combinations and numbers seems to be most effective in speeding passage through the to make thousands of different types of proteins. During diges- colon, which may reduce the risk of colon cancer. Psyllium tion, proteins are broken down into their component amino

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Table 10.1 Table 10.2 Functions of Proteins Essential and Nonessential Amino Acids

Type of Protein Function Examples Essential Nonessential Structural Support Collagen, keratin Histidine Alanine Enzymes Catalysts Digestive enzymes Isoleucine Asparagine Hormones Regulation Insulin Leucine Aspartic acid Transport Transport Hemoglobin Lysine Arginine substance Methionine Cysteine Storage Storage of amino Ovalbumin in egg Phenylalanine Glutamic acid acids white, casein in Threonine Glutamine milk Tryptophan Glycine Contractile Movement Actin and myosin Valine Proline in muscles Serine Defensive Protection Antibodies (immunoglobins) Tyrosine

acids by enzymes in the digestive tract and transported in the Table 10.3 Protein Content (in grams) bloodstream to the liver and body tissues. of Some Common Food Items Essential Amino Acids 1 ounce meat (beef, chicken, turkey) . . . . . 7 The necessary role of dietary proteins is to supply amino 1 ounce cheese ...... 7 acids, so that the body can construct human proteins. All 1 glass milk ...... 8 20 amino acids are necessary for protein synthesis, and cells 1/2 cup beans ...... 6 in the human body have the ability to synthesize 11 amino 1 slice whole-wheat bread ...... 4 acids from raw materials; the other nine cannot be made 1 egg ...... 8 by the body. These nine are called the essential amino acids 2 tbsp. peanut butter ...... 8 (table 10.2 and see fig. 1.6) and must come from the diet. It is 1 serving oatmeal ...... 5 important to note that these essential amino acids cannot be stored by the body. For this reason it is critical that the body receive all the essential amino acids in a single day. Persistent diet should have 50 grams of protein per day; those on a lack of these essential amino acids prevents synthesis of neces- 1,600-kilocalorie diet, 40 grams of protein per day; and those sary proteins and results in protein-deficiency diseases. on a 2,200-kilocalorie diet, 55 grams of protein. The following daily protein intakes have been recommended for specific Complete Proteins age groups: infants under 1 year—14 grams; children 1 to 4 Complete proteins contain all the essential amino acids and years old—16 grams; pregnant women—60 grams; and nursing in the right proportions. Almost all proteins derived from mothers—65 grams. The protein we require can be obtained animals are complete proteins, whereas proteins derived from from many foods. Table 10.3 contains examples of the protein plants are usually incomplete, deficient in one or more essen- content of some common foods. tial amino acids. Although plant proteins are incomplete, the Proteins can be assigned a numerical value that reflects essential amino acid requirements can be met by combining how well they supply the essential amino acids. The protein complementary plant proteins. For example, the traditional in eggs has been assigned a biological value of 100, and all diet of the native peoples of Mexico, beans and corn, contains other foods are given values using egg protein as the reference complementary protein sources. The beans are low in methi- standard. Another factor that needs to be considered is the onine but adequate in tryptophan and lysine, but corn, which digestibility of a particular protein. Some proteins cannot be is poor in tryptophan and lysine, contains adequate amounts broken down completely; that is, the amino acids are not fully of methionine. released during digestion. This incomplete breakdown reduces Although we have an absolute requirement for the the dietary value of the protein. For example, when digestibility essential amino acids, the actual amount of protein required is taken into account, even egg protein, considered the perfect by humans is a small percentage of our nutrient needs. It is protein source, drops to a value of 94. High-quality proteins con- recommended that approximately 10% (a range from 8% to tain all the essential amino acids in the right proportions and 10%) of our total caloric intake be provided by proteins. On are fully digestible, freeing their amino acids, which are then the basis of this percentage, individuals on a 2,000-kilocalorie absorbed into the blood and transported to the body’s cells.

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gastrointestinal tract and are eventually eliminated in the feces. In patients with celiac disease, gluten penetrates the Thinking Critically small intestine, eliciting an immune response, which damages Humans have a dietary requirement for proteins, although the cells in the lining. proteins are needed in smaller quantities than carbohy- It has been discovered that patients with celiac disease drates and fats. have abnormally high permeability of the intestinal wall. The cells of the intestinal lining are joined together by tight junc- On the basis of caloric intake, determine your protein tions, complexes of proteins that join adjacent cells to form requirement. a permeability barrier. Tight junctions prevent most materi- als from moving through the spaces between the cells and penetrating the lining of the small intestine to reach deeper tissues. However, in the normal functioning of the body, there Gluten and Celiac Disease are circumstances in which this barrier must be breached to Eating gluten, the major protein in wheat, or the related allow for the passage of large molecules or cells. Zonulin is proteins secalin and hordein, in rye and barley, respectively, the body’s protein that, when released, increases intestinal wall (see Chapter 12), can trigger celiac disease in individuals who permeability. Apparently, the amount of zonulin is abnormally have an inherited sensitivity to these proteins. Celiac disease high in patients with celiac disease, and this allows gluten to is characterized by destruction of the intestinal lining and pass through the gut wall. recurrent abdominal pain and diarrhea. In the most serious The immune system is programmed to react to f oreign cases, the body is unable to absorb nutrients. Aretaeus, a proteins that may signal the arrival of disease-causing micro- Greek physician who practiced during the first century a.d., organisms. Eating food is one way foreign proteins are intro- was the first to describe children who, while apparently well duced into the body. Immune cells are situated beneath the fed, were nonetheless exhibiting signs of starvation. In 1887, lining of the small intestine, primed to attack any foreign the English physician Samuel Gee observed that the condition proteins that pass through the intestinal lining. Ninety-five per- of chronic indigestion could affect people of all ages but was cent of those suffering from celiac disease have certain genetic especially prevalent in children of 1–5 years old. Willem- markers on their cells, either HLA-DQ8 or HLA-DQ2 or Karel Dicke, a Dutch pediatrician, was the first to link the both. These protein molecules pick up the peptide fragments condition of chronic indigestion to wheat gluten during World of gluten and present them to T cells, a type of immune cell. War II. He observed that, during times of bread shortages in These T cells are now trained to attack and destroy the gluten the Netherlands, children with celiac disease were no longer fragments whenever they are encountered. As the T cells dying, but the mortality rate returned to the pre-war level of destroy the gluten fragments, cells in the intestinal lining are 35% when bread was once more plentiful. damaged, causing the gastrointestinal symptoms of celiac A newly available blood test has enabled physicians to disease. Additionally, it has been discovered that sufferers of more clearly identify sufferers of celiac disease. When intes- celiac disease also release immune-stimulating chemicals that tinal cells are damaged, an enzyme called transglutaminase intensify the immune response. is released. Evidence of elevated levels of transglutaminase in Patients who suffer from celiac disease apparently also the blood is indicative of celiac disease. In 2003, a widespread have certain abnormalities in their small intestine. Repeated screening trial revealed that the incidence of celiac disease in exposure to gluten in patients with celiac disease causes the North America is about 1 in 133, a ratio that indicates that the villi of the small intestine to become chronically inflamed. affliction is 100 times more common than thought previously. Villi, fingerlike projections in the lining of the small intestine, It may seem puzzling that the human body would react in such absorb digested nutrients from the gut and pass them into the an abnormal way to the protein in wheat, a staple food for circulatory system for distribution. In celiac disease, the villi much of humanity, but it is important to realize that wheat and become damaged and flattened, which decreases the surface other cereal grains were not part of the original human diet. area of the small intestine and its ability to absorb nutrients. Our ancestors subsisted primarily by foraging for sweet fruits, Undiagnosed patients are often thought to be suffering from starchy tubers, seeds of legumes, and eggs and by hunting other conditions, such as osteoporosis or chronic fatigue, but animals for the occasional meat meal until agriculture arose the underlying cause is impaired nutrient absorption because approximately 10,000 years ago (see Chapter 11). of celiac disease. When patients with celiac disease eliminate Celiac disease is an autoimmune disorder in which the gluten from their diet, the villi resume their original shape and immune system of genetically predisposed individuals reacts function normally. abnormally to the presence of gluten. Gluten is made up of The primary treatment for celiac disease is to remove the large amounts of glutamine and proline, amino acids for which gluten trigger by eating a gluten-free diet. Another promising the body lacks the enzymes to digest completely. Instead, the strategy is to administer enzymes that would break down gluten is broken down into peptides, small protein fragments, completely any gluten present in the small intestine. Other containing these amino acids. Normally, these peptides are potential strategies are to depress the immune response or not absorbed by the small intestine but remain inside the desensitize the immune system by introducing small, repeated

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exposures to gluten. Some researchers recommend that infants born to a family with an incidence of celiac disease have a Table 10.4 gluten-free diet during their first year. By preventing exposure Functions of Lipids during the period of rapid development of the immune system, gluten sensitivity might be avoided. Another promising tactic Type of Lipid Function Examples is to develop drugs that are zonulin inhibitors to reduce the Triglyceride Energy, storage Animal fat, vegetable permeability of the intestinal lining in celiac patients. oils Researchers are also working to develop gluten-free vari- Insulation Subcutaneous fat eties of wheat that would be safe to eat for people who suffer Steroid Structure Cholesterol in from celiac disease. Recently a mutant form of barley was membranes isolated that completely lacked the gliadin-like protein found in Hormonal Cortisol, estrogen, gluten but was high in lysine, one of the essential amino acid regulation testosterone which is usually deficient in wheat flour. Gliadin is the pri- Phospholipid Structure Phosphatidylcholine in mary culprit in celiac disease and researchers are hopeful that cell membranes the gliadin-free barley will be the start of developing gluten-free wheat varieties that will retain all of the flavor and baking qualities associated with wheat flour. Research has shown types of fatty acids can occur. It is the nature of the fatty acids previously that eliminating gliadins from gluten does not affect that determines the chemical and physical properties of the tri- the bread-making qualities of wheat flour. It is also known that glyceride. Each fatty acid contains a carbon chain with hydro- heirloom varieties of wheat such as einkorn, emmer, and spelt gen attached to the carbon atoms; different fatty acids vary in (see Chapter 12) are much lower in gluten content and may the number of carbon and hydrogen atoms. also be used to develop gluten-free wheat varieties. During digestion in the small intestine, triglycerides are first acted on by bile, which is made by the liver and stored and released by the gallbladder. Bile contains a complex mixture of lipids, bile salts, and pigments; prominent among the lipid Thinking Critically components are cholesterol and lecithin. Bile acts as an emul- Some people apparently develop celiac disease not as sifier, breaking up the triglycerides into smaller droplets that infants but much later in life. It has been suggested that the can be acted on by enzymes. Enzymes from the pancreas and delay of celiac disease in genetically predisposed individuals intestinal cells split these smaller droplets of triglycerides into is due to changes in the population of bacteria that normally monoglycerides and two fatty acids or into glycerol and three inhabit the gut. fatty acids. These end products are absorbed into the intestinal cells, where they are resynthesized into new triglycerides that What might the bacteria population be supplying to the enter the lymphatic system and eventually the bloodstream. host that has forestalled the activation of the immune High blood triglyceride level is a risk factor for coronary heart system to attack gluten? Does this suggest another disease. possible treatment for sufferers of celiac disease? Essential Fatty Acids The body is capable of synthesizing most fatty acids, but three must be supplied in the diet. Linoleic, linolenic, and Fats and Cholesterol arachidonic acids are designated essential fatty acids, but few Fats are usually considered culprits in the diet because they adults suffer deficiency symptoms because these three fatty are associated with cardiovascular disease, but some fat is acids are widely found in foods, especially vegetable oils. Even necessary because it serves several vital functions and some if an adult were consuming a totally fat-free diet, as little as fats are heart-healthy. Fats and related compounds belong to a 1 teaspoon of corn oil, as an ingredient in foods, would supply larger category of organic molecules called lipids. Although a the essential fatty acids. Deficiency symptoms, such as poor diverse group of compounds, all lipids share the characteristic growth and skin irritation, have been seen in infants fed a of insolubility in water (table 10.4). formula lacking these essential nutrients.

Triglycerides Saturated and Unsaturated Fats Ninety-five percent of the lipids in foods are fats and oils; both Fatty acids can be separated into two types, saturated and these compounds are chemically classified as triglycerides , unsaturated. Saturated fatty acids contain all single bonds which are formed from glycerol and three fatty acids (see between the carbon atoms and have the maximum number fig. 1.12). Fatty acids themselves are the simplest type of lipid of hydrogen atoms (it is said to be saturated with hydrogen). and serve as building blocks for triglycerides and phospholipids. Unsaturated fatty acids have one or more double bonds A glycerol backbone is common to all triglycerides, but many between carbon atoms and consequently fewer hydrogen

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H H H H H H H H H H H H H H H H H O Coconut H C C C C C C C C C C C C C C C C C C OH Palm kernel H H H H H H H H H H H H H H H H H Butter Stearic acid, a saturated fatty acid. Table cream Cocoa butter H H H Beef tallow H CC H C C H H C Palm H C H H C H H C H H H C H C H Lard H C H C H H C H C H H ** C H C Sunflower H H C O C H H H Olive

H OH Fat or oil Avocado Oleic acid, a monounsaturated fatty acid with double bond in cis configuration. Almond Canola HHH H H H Peanut H C CC CCH H C C H H Soybean H C C H H H H C C H H Corn H H C C H H C C H H Walnut H C H H H H C O 0102030405060708090 100 H C OH Fatty acid composition (%)*

Linoleic acid, a polyunsaturated fatty acid. Saturated Both double bonds are in the cis configuration. Monounsaturated Figure 10.1 Structure of a saturated, monounsaturated, and Polyunsaturated polyunsaturated fatty acid. Other lipids

atoms. Each carbon atom can form only four bonds, so if a Figure 10.2 Fatty acid composition in common fats and oils. double bond occurs between two carbons, then less than the *Calculated as a percent of total lipids. **Newer varieties of sunflower and safflower produce oils which are 70% oleic acid, full complement of hydrogen atoms can be attached. A fatty a monounsaturated fatty acid. acid with one double bond is called monounsaturated and lacks Source: Data from USDA National Nutrient Database for Standard Reference. two hydrogen atoms; a polyunsaturated fatty acid has two or more double bonds and lacks four or more hydrogen atoms (fig. 10.1). The health implications of saturated versus unsaturated All food fats contain a mixture of both saturated and fats have been intensely studied by the scientific community. unsaturated fatty acids (fig. 10.2). Saturated fats contain Because saturated fats increase blood cholesterol levels, they mostly saturated fatty acids and are solid at room tempera- are linked to cardiovascular diseases. Unsaturated fats, on the ture; animal fats, such as lard, butter, and beef fat, are familiar other hand, lower the risk of cardiovascular disease by lower- examples. Vegetable oils are generally composed of unsaturated ing blood cholesterol levels. fatty acids and are liquid at room temperature. Oils containing mostly monounsaturated fatty acids are olive oil, peanut oil, Cholesterol and canola oil; other vegetable oils, such as corn oil, soybean Cholesterol belongs to a subcategory of lipids known as ste- oil, and walnut oil, contain mostly polyunsaturated fatty acids. roids, which are compounds containing four carbon rings (see Coconut oil, palm and palm kernel oils, and cocoa butter are Chapter 1). Several steroids, including cholesterol, also have exceptions to the rule. Although they are of plant origin, they a hydrocarbon tail and an —OH group, making them sterols. consist mostly of saturated fatty acids. On the other hand, cer- Cholesterol is a vital constituent of cells; it is part of the lipid tain fish oils are actually unsaturated. The oils from fish such component of cell membranes and is used in the synthesis of as salmon, tuna, and herring are polyunsaturated and contain sex hormones and several other hormones. omega-3 fatty acids. Omega-3 fatty acids lower the tendency of Cholesterol is synthesized in the liver from saturated fatty blood platelets to stick together and form blood clots. Lowering acids and is absorbed by intestinal cells from animal foods, the risk of clot formation reduces the incidence of blocked especially eggs, butter, cheese, and meat. If the diet is high in blood flow to the heart and the onset of coronary heart disease. saturated fats, even if it is low in cholesterol, the liver responds

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by increased cholesterol synthesis. Because cholesterol, like transport, and thereby reduce the risk of cardiovascular dis- all lipids, is insoluble in the watery medium of the blood, it is ease. Older HDL particles may no longer be capable of reverse transported by a special complex that consists of a cholesterol cholesterol transport. Newer strategies aim to develop medi- center with a coating of lipids and water-soluble proteins. cations that raise only the young, functional HDL particles. These transport molecules, known as lipoproteins, exist in sev- eral forms. Two of the most significant are the low-density lipo- proteins (LDLs) and high-density lipoproteins (HDLs). LDLs Trans Fatty Acids transport cholesterol to all the body cells, while HDLs remove Trans fatty acids that occur naturally in foods such as beef, excess cholesterol from the body’s tissues and carry it to the lamb, whole milk, cream, and butter are derived from rumi- liver for degradation and elimination. In the popular press, the nant (cud-chewing) animals. Conjugated linoleic acid, a nat- LDLs are considered the “bad” cholesterol because they can ural trans fatty acid, may be beneficial as an anticarcinogen be taken up by the cells that line the arteries. The resulting and in strengthening the immune system. However, most deposition of cholesterol blocks the arteries, restricting the trans fatty acids are made when manufacturers convert liquid blood flow and is known as atherosclerosis. This condition can oils into solid fats. In this practice, known as hydrogenation, lead to heart attacks if the coronary arteries are blocked and vegetable oils are partially or fully hydrogenated to make mar- strokes if the arteries delivering blood to the brain are blocked. garine, vegetable shortening, peanut butter, and salad dressing. HDLs are considered “good” cholesterol because they can pre- Trans fats are present in many processed foods, such as crack- vent atherosclerosis by preventing the buildup of cholesterol ers, cookies, baked goods, snack foods, and practically any deposits on the lining of the arteries. food made with or fried in partially hydrogenated oils. Diets high in cholesterol, saturated fat, or both contrib- Trans fats act somewhat like saturated fats, but chemi- ute to high blood cholesterol levels, especially in the form cally, trans fats are unsaturated. The carbon-carbon double of LDLs. Plant sources do not contribute dietary cholesterol bonds found in unsaturated vegetable oils are in a cis configu- directly, although, as pointed out previously, some are high in ration in which the molecular groups attached to each carbon saturated fats. On the other hand, plant oils are generally rich in the double bonds bend in the same direction, either both in unsaturated fats, which are known to lower blood choles- up or both down. During the hydrogenation process, some terol levels. However, monounsaturated and polyunsaturated of the double bonds are broken and hydrogen is added to the fats act differently. Polyunsaturated fats tend to lower all cho- carbons. More significantly, most of the double bonds change lesterol levels, including the protective HDLs, whereas mono- configuration from cis to the trans position. In the trans config- unsaturated fats raise the HDLs while lowering total and LDL uration, the molecules attached to each carbon of the double levels. LDL blood cholesterol level is a better gauge of the bonds bend in opposite directions or in a zigzag fashion. Thus, risk of heart disease than is total blood cholesterol; the lower trans fatty acids can stack closer together, and the transformed the LDL level, the lower the risk of heart disease. Cholesterol oil readily takes on a solid, spreadable form that many consum- ratio, the ratio of total cholesterol to HDL, is another measure ers prefer over the natural liquid state. for the risk of heart disease. The ratio should be less than 5 A study of elderly men in the Netherlands indicated that a to 1; the recommended ratio is 3.5 to 1 or lower. Although diet high in trans fat raised blood LDL cholesterol levels while hereditary factors, cigarette smoking, and exercise play a role lowering HDL levels. Coronary heart disease was higher in in the LDL-HDL balance, for the majority of people diet is the those men who ate more trans fats, and the risk of developing single most important factor in controlling cholesterol levels coronary heart disease within 10 years increased by 25% for and the inherent disease risks. each additional 2% of trans fats consumed in their diet. After The HDL hypothesis suggests that raising HDL and low- 10 years, the percentage of trans fats in the diets of these men ering LDL levels should lower the risk of cardiovascular dis- dropped from a high of over 4% to just less than 2%. It is ease, but recent findings contest this idea. For example, people estimated that trans fats make up about 2%–4% of the typical with certain genetic mutations that raise HDL levels were U.S. diet. studied and were found not to have the expected reduced risk In the Nurses’ Health Study, conducted by the Harvard of cardiovascular disease. Also, people who have a different School of Public Health, nearly 90,000 women filled out mutation that lowered the level of HDL to about half of what detailed questionnaires about their diet every few years for is seen in the general population were found to have a lower, 14 years. The results found no correlation between the onset not higher, risk of cardiovascular disease as compared to the of type 2 diabetes and the total fat, saturated fat, or mono- general population. In addition, during testing of a proposed unsaturated fat consumed. There was, however, a significant drug that raised HDL levels from 30% to 100%, the risk of occurrence of this most common type of diabetes when the cardiovascular disease was not lessened but actually increased women had diets high in trans fats. It was also discovered that in some individuals. a diet high in polyunsaturated oils lowered the risk of type 2 The problem may be that not all HDL function similarly. diabetes. It has been suggested that only young HDL can remove cho- Since 1983, the FDA has required that saturated fat lesterol that has built up in artery walls and deliver it to the and dietary cholesterol be listed on food labels. Due to the liver for elimination, a process known as reverse cholesterol apparent association between high trans fats in the diet and

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the higher risk of cardiovascular disease and, in females, type 2 diabetes, the content of trans fats must be listed on the Table 10.5 Nutrition Facts panel of food labels in the United States. Fat-Soluble Vitamins Manufacturers have responded to health concerns and consumer demand by developing new methods of hydroge- Vitamin Dietary Source Results of Deficiency nating vegetable oils. Using supercritical carbon dioxide as A Yellow, orange, and Night blindness, a solvent and under conditions of higher pressure and lower dark green vegetables xerophthalmia temperatures, USDA researchers produced a hydrogenated and fruits; dairy soybean oil with only 10% trans fats. This percentage is lower products than the usual 10%–30% trans fats found in most hydrogenated D Eggs and enriched Rickets vegetable oils. dairy products E Seeds, leafy green Unknown vegetables K Leafy green vegetables Poor blood clotting MICRONUTRIENTS Like macronutrients, micronutrients are essential for proper nutrition, but they are required in much smaller amounts. Table 10.6 While macronutrients make up the bulk dry weight of food, micronutrients constitute only 1%–2% of the dry weight. There Water-Soluble Vitamins are two categories of micronutrients, the organic compounds known as vitamins and the inorganic compounds, the minerals. Results of Vitamin Dietary Source Deficiency

B1 (thiamine) Whole grains, Beriberi Vitamins legumes, seeds, nuts Many vitamins play roles as coenzymes (molecules that are B2 (riboflavin) Dairy products, whole Mouth sores, required for the proper functioning of certain enzymes) in grains, leafy green lesions of eyes many metabolic pathways in the body; others are directly vegetables, poultry involved in the synthesis of indispensable compounds. Niacin Meat, eggs, seeds, Pellagra Vitamins are classified according to their solubility, with four legumes

fat-soluble vitamins (A, D, E, and K) and nine water-soluble B6 (pyridoxine) Dried fruits, seeds, Irritability, vitamins (eight B-complex vitamins and C). The water-soluble poultry, leafy green muscle vitamins are not readily stored in the body, and any excess is vegetables weakness, skin eliminated in the urine; therefore, these are unlikely to become disorders toxic. On the other hand, the fat-soluble vitamins are easily Pantothenic acid Dried fruits, seeds, Insomnia, stored in the fatty tissues of the body, and excessive intake can poultry, leafy green weakness lead to toxicity symptoms. The dietary sources and deficien- vegetables, nuts cies of these vitamins are described in Tables 10.5 and 10.6. Folic acid (folate) Legumes, whole Anemia, The following discussion is limited to vitamins A, D, and C grains, green diarrhea, neural vegetables tube defects and the B vitamins thiamine, niacin, and B12. Biotin Legumes, vegetables, Fatigue, meat, egg yolks dermatitis Vitamin A B12 (cobalamin) Meat, eggs, dairy Pernicious Vitamin A has many roles in the body. One of the best known products anemia involves the formation of vision pigments (rhodopsin and oth- C Fresh fruits and Scurvy ers) present in the retina of the eye. Each pigment is composed vegetables of a molecule of retinal (a form of vitamin A) and a protein molecule, called an opsin, that differs from pigment to pig- ment. The pigments are contained in two types of photorecep- area roughly equivalent to one-fourth of a football field. When tor cells, rods and cones, located deep in the retina of the eye. vitamin A is lacking, these tissues fail to secrete their protec- All light stimulates the rods, providing only black-and-white tive mucus covering, producing instead a protein called keratin vision, while the cones are selectively stimulated by different (normally found in hair and nails), which results in the tissues’ colors, providing the full spectrum of color vision. In dim light becoming dried and hardened. This aspect of vitamin A defi- or at night, only the rods are used for vision; therefore, a short- ciency can therefore affect many different areas in the body. One age of retinal has especially pronounced effects, leading to one of the most tragic consequences is a type of blindness known as of the earliest signs of vitamin A deficiency, night blindness. xerophthalmia, in which severe vitamin A deficiency results in Vitamin A is also necessary for the maintenance of epithe- irreversible drying and degeneration of the cornea. This perma- lial tissues that line both internal and external body surfaces, an nent blindness, easily preventable with proper nutrition, is found

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most frequently among malnourished children in developing Other model organisms have showed similar results. Some nations. In the skin, keratinization results in rough, dry, scaly, strains of mice were genetically engineered to produce higher and cracked skin, often with an accumulation of hard material than normal levels of antioxidant enzymes, whereas other around a hair follicle that looks like a permanent goose bump. strains were created that produced lower than normal levels Other epithelial tissues, such as those in the mouth, gastrointesti- of antioxidant enzymes. It was expected that the mice with nal tract, and respiratory system, are also affected by the decrease higher levels of antioxidant enzymes in their bodies would live in mucus production, becoming progressively drier and subject to longer that those with lower levels but there was no difference infection. Vitamin A is additionally involved in dozens of other in life spans between the strains. Observations from nature roles in the body, including normal bone and tooth development also support the experimental data. The naked mole rat with and hormone production in the adrenal and thyroid glands. lower levels of natural antioxidants and evidence of more oxi- In food derived from animal sources, especially liver, dative damage to their bodies lives 25–30 years, about eight vitamin A occurs primarily as retinol, which is readily absorbed times longer, than another rodent, the common mouse. by the body and converted to retinal. In plant sources, no ret- As antioxidants have been shown to not always be benefi- inol is present, but a vitamin A precursor, beta-carotene (first cial, new research is indicating that free radicals are not always isolated from carrots) occurs abundantly in many yellow, harmful. At lower levels, free radicals appear to signal the orange, and dark green fruits and vegetables (see Chapter 3) body to turn on genes to repair oxidative cellular damage and and can be split into two molecules of retinol in the body. prevent further injury. Free radicals have been shown to acti- vate gene HIF-1 which itself turns on genes that are involved in cellular repair. Current research is suggesting that at lower Antioxidants levels free radicals are not necessarily destructive agents in The importance of beta-carotene as an antioxidant has been themselves but are instead signals to the body to turn on genes investigated. Antioxidants may protect the body against to repair oxidative cellular damage and prevent further injury. the destructive action of reactive ions called free radicals. Only, in larger amounts, free radicals destructive. Destructive free radicals form when electrons escape from the Electron Transport System during ATP production and com- bine with oxygen available in mitochondria (see Chapter 4). Vitamin D These highly reactive ions can damage the metabolic machin- The primary function of vitamin D is the regulation of calcium ery of the cell, impairing energy production. They may also and phosphorus levels, especially for normal bone devel- damage DNA itself, inducing mutations, and they have been opment. Vitamin D helps control the blood levels of these implicated in cancer, heart disease, and even the signs of aging. minerals in three ways: Several recent animal studies are challenging the prevail- 1. the absorption of calcium and phosphorus from food in the ing concept that the build-up of free radicals, destructive ions gastrointestinal tract, that produce oxidative damage in cells, accounts for many 2. the removal of these minerals from bones to maintain the of the deleterious effects associated with aging. There is also concentration in the blood, and recent evidence that the practice of taking antioxidant supple- 3. the retention of calcium by the kidneys. ments to neutralize the effects of free radicals can be harmful. Researchers bred roundworms (Caenorhabditis elegans) to over- Vitamin D is unique in that it can be synthesized by the produce a specific free radical (superoxide) with the expectation human body on exposure to sunlight; in fact, it has long been that the worms would die prematurely compared to worms with called the sunshine vitamin. The precursor (a cholesterol lower levels of this free radical. Surprisingly, the worms which derivative) is manufactured by the liver and transported to the had higher levels of the free radical, lived 32% longer. More skin, where exposure to the sun’s ultraviolet rays converts it astonishing, treating the worms with high levels of free radicals to provitamin D; the final steps in the manufacture of active with the antioxidant vitamin C reversed the longer life span. vitamin D occur in the liver and kidneys. The amount of In another group of experiments with roundworms, pigmentation in the skin affects the synthesis of vitamin D normal worms were exposed to an herbicide that is known because pigment blocks ultraviolet absorption. Darker skin to induce free radical production in animals. The herbicide requires longer exposure to sunlight to produce adequate treated worms, with the higher level of free radicals, lived amounts of vitamin D. Thirty minutes of sunlight is adequate almost 60 percent longer than untreated worms; and once for light skin, while darker skin may require up to 3 hours. This again feeding antioxidants to the worms prevented this lon- exposure to sunlight must be achieved with caution, since over- gevity. Researchers then genetically engineered roundworms exposure to the ultraviolet rays in sunlight is linked to higher without the ability to produce certain natural enzymes that risk of skin cancer. The Environmental Protection Agency has act as antioxidants. As anticipated, the genetically engineered estimated that the average American is indoors 93% of the worms had higher levels of free radicals and more potentially time, in transit 5% (cars, buses, trains), and outdoors only 2% damaging oxidative reactions throughout their bodies but of the time daily. This limited exposure to sunlight makes it unexpectedly the worms did not age prematurely but instead essential that the diet contain vitamin D to avoid deficiency lived just as long as worms with normal levels of antioxidants. symptoms. Vitamin D is not naturally abundant in any food.

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to sunlight is the lowest. Recent studies have correlated blood levels of vitamin D in women to colon cancer. Those with the lowest blood levels of the vitamin had double the risk of colon cancer compared with those women who had the highest lev- els of vitamin D. Preliminary research shows that this trend may also be repeated for type 2 diabetes and other diseases. Excess vitamin D causes abnormally high levels of calcium in the blood; this condition often leads to calcium deposits in soft tissues, such as kidneys and blood vessels. If not caught in time, this may result in irreversible damage to the cardiovascular system, kidney failure, and even death. In excess, vitamin D is the most toxic of all the vitamins. However, this toxicity cannot occur from sunlight or food; it results only when megadoses of the vitamin are administered without medical supervision. Source: Center for Disease Control and Prevention Disease Control Source: for Center

Figure 10.3 Characteristic bowing of the legs and knees in Vitamin C rickets, a disease caused by insufficient vitamin D. Fresh fruits and vegetables are the richest sources of vitamin C, ascorbic acid, with organ meats the only significant animal None occurs in plant sources, but vitamin D does occur in lim- sources. The most important role of vitamin C in the body ited amounts in animal sources, such as egg yolks, liver, cream, is in the synthesis of collagen, a connective tissue protein some fish, and butter. Because there is concern about meeting that serves as a “cellular cement,” holding cells and tissues the nutritional needs for vitamin D, especially for children, together. Collagen, the most abundant protein in the body, is milk, which does not contain adequate vitamin D, is routinely found in the matrix of bones, teeth, and cartilage and provides fortified with this vitamin. the elasticity of blood vessels and skin. Vitamin C also func- Because of the role of vitamin D in calcium regulation, tions as an antioxidant in the body, preventing other molecules the deficiency symptoms are most evident in bone formation. from being oxidized (losing electrons). Because vitamin C The effects of vitamin D deficiency are most pronounced prevents oxidation, it is sometimes added to packaged foods in children and result in a characteristic malformation of to extend the shelf life; in a similar manner, orange juice and the skeleton known as rickets. The bowing of the legs so lemon juice, with their high vitamin C content, prevent the commonly associated with the condition is just one of many oxidation (browning) of sliced apples and bananas. Vitamin C abnormalities of the skeletal system (fig. 10.3). Dark-skinned is additionally involved in promoting iron absorption through children who live in northern, smoggy cities are especially the intestines. When foods containing vitamin C are con- vulnerable to developing this deficiency. Once believed to have sumed with foods containing iron, absorption is enhanced. been eradicated in developed countries, rickets has reemerged Finally, vitamin C is involved in a number of other metabolic in the United States and the United Kingdom. The problem reactions, including the production of various hormones. seems to be that breastfed children are not receiving enough For centuries, sailors on long ocean voyages faced the vitamin D to absorb the amount of calcium necessary to build possibility of developing scurvy, a disease that could cause strong bones and teeth. Pediatricians are now recommending bleeding of the gums, pinpoint hemorrhages under the skin, vitamin D supplements for breastfed infants. Adult rickets, severe fatigue, poor healing of wounds, brittle bones, and even also known as osteomalacia, is rare but does occur in women sudden death due to massive internal bleeding. It was not who have undergone repeated pregnancies, have low calcium uncommon for half to two-thirds of the ship’s company to die intake, and have inadequate exposure to sunlight. However, of scurvy on a long voyage. The first cure for this disease was a large scale study in 2018 found no benefit in the taking of identified in 1747 by Dr. James Lind, who experimented with high—dose vitamin D supplements in either increasing bone 12 sailors afflicted with scurvy. Lind tried various dietary sup- density or in the prevention of fractures from falls. plements and found that sailors who were given either oranges Currently, some researchers in nutrition are advocating or lemons for 6 days improved rapidly. Interestingly, it was that the daily recommended dose of vitamin D be raised to almost 50 years after these findings that the British admiralty 1,000 IU* (International Units) per day for adults not only to took measures to prevent scurvy by dictating that all sailors promote healthy bones but also to prevent certain forms of receive lemon or lime juice daily. (British sailors were soon cancer. Previous studies have shown that colon cancers are nicknamed “limeys” because of this practice, a name that is more prevalent in the northern United States where exposure still heard today.) Now it is well known that the vitamin C in citrus juice prevents scurvy. The typical symptoms of scurvy can be traced directly to the inability of the body to make *International Unit is a unit of measurement for biologically active substances (such as vitamins, hormones, and vaccines) that produces a measured biological effect agreed collagen. The scurvy–vitamin C connection is reflected in the upon as an international standard. name ascorbic acid, which literally means “without scurvy.”

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Since the 1970s, the daily intake of vitamin C has been found mainly in Asia, where diets were based mainly on polished the focal point of a heated debate, after the publication of or white rice rather than on the whole-grain brown rice that still Vitamin C and the Common Cold by Linus Pauling, a Nobel has the outer bran (husk) intact. The thiamine that occurs in the Prize–winning chemist. The RDI (reference daily intake)** for outer layer of the rice is removed during the polishing process. vitamin C is 60 milligrams (approximately 10 milligrams daily Beriberi became more prevalent when improved techniques for can prevent scurvy), but Pauling recommended megadoses polishing rice were developed that removed more of the bran as high as 2,000 to 10,000 milligrams for optimum health. and, inadvertently, more of the thiamine. In the 1880s, thiamine Pauling maintained that large doses of vitamin C can prevent deficiency in the Japanese navy was particularly widespread, colds and other viral infections and that vitamin C is bacteri- with 25%–40% of the sailors developing beriberi. A Japanese cidal and even cures cancer. Recent research has shown that physician, Dr. K. Takaki, observed that few sailors developed high doses of vitamin C is effective in killing certain types of the disease when milk, meat, and eggs were added to the nor- colon cancer cells. However, some authorities note that tissues mal staple of white rice. Unfortunately, he did not realize that become saturated with vitamin C at levels of 80 to 100 milli- the enriched diet was supplying a nutrient missing in the white grams per day and that intakes above these levels are generally rice diet. A few years later, a Dutch physician, Dr. Christiaan excreted in the urine. Controversy also exists regarding the Eijkman, studied beriberi in the East Indies; he showed that, in toxicity of vitamin C. Some scientists maintain that high doses diets based almost exclusively on rice, the consumption of brown are nontoxic; others feel that toxicity can occur. The most rice instead of white rice prevents the appearance of beriberi. common toxicity symptoms are nausea, abdominal cramps, It was not until the twentieth century that thiamine deficiency and diarrhea. Another possible complication of megadosing was actually identified as the cause of the disease. Good dietary is rebound scurvy, a condition that may occur after an abrupt sources of thiamine include meat, especially pork and liver, cessation of these high doses. Symptoms mimic scurvy, even whole grains, seeds and nuts, and legumes. though vitamin C intake is not deficient; these symptoms do not occur if the megadoses are decreased gradually. Niacin Niacin is the collective term for two compounds, nicotinic acid and nicotinamide, either one of which is used + + Vitamin B Complex to form the coenzymes NAD and NADP . Recall the impor- tance of these coenzymes for oxidation-reduction reactions The vitamin B complex includes a group of eight vitamins that in many energy-yielding metabolic pathways (see Chapter 4). are often found in foods together and have similar roles in the Without these coenzymes, the release of energy from the body; that is, they function as coenzymes, involved in thou- breakdown of foods cannot occur and cellular death results. sands of metabolic reactions. They are found in each cell of Niacin can be supplied directly through foods rich in niacin the body and must be present for normal cell functioning. For itself or foods rich in the essential amino acid tryptophan each of these vitamins, specific deficiency symptoms occur because the body can synthesize niacin from the amino acid. when the vitamin is lacking in the diet, but in general, no toxic- Niacin deficiency, therefore, is coupled with a low-protein diet. ity symptoms have been reported because excess is excreted in A lack of niacin severely affects every organ of the body, the urine. As is vitamin C, the B vitamins are water soluble and and a severe deficiency disease, pellagra, develops. The symp- can be leached out during food preparation when excess water toms of pellagra are referred to as the 4 Ds: dermatitis (skin is used and discarded. In addition, some of the B vitamins may disorders), dementia (mental confusion), diarrhea, and eventu- be destroyed by high temperatures during cooking. Thiamine, ally death if niacin is not supplied. The dermatitis (fig. 10.4) is niacin, and B12 will be considered because these vitamins may characterized by rough, reddened skin with lesions developing be deficient in plant sources.

Thiamine Thiamine, also known as vitamin B1, is part of the coenzyme thiamine pyrophosphate, which is involved in the met- abolic breakdown of carbohydrates just before the Citric Acid Cycle. Because of thiamine’s central role in metabolism, the symptoms of thiamine deficiency are profound: fatigue; depres- sion; mental confusion; cramping, burning, and numbness in the legs; edema; enlarged heart; and eventually death from cardiac failure. This thiamine deficiency is known as beriberi and was

**Daily values are determined by the U.S. FDA (Food and Drug Administration) and indicate the percentage amount of a nutrient that is provided by a single serving of a particular food, based on the current recommendations for a 2,000-kilocalorie diet. There are two categories of daily values: daily reference values (DRVs) and reference daily intakes (RDIs). DRVs have been determined for total fat, saturated fat, cholesterol, and Prevention Disease Control Source: for Center total carbohydrate, dietary fiber, sodium, potassium, and protein. RDIs are established for 19 vitamins and minerals and have replaced the older term recommended daily Figure 10.4 Pellagra, caused by a lack of niacin, is allowances (RDAs). characterized by dermatitis of the hands.

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in exposed areas; in fact, pellagra means “rough skin.” The cen- after the age of 60, when intrinsic factor production becomes tral nervous system is affected, and confusion, memory loss, impaired. In this case, B12 deficiency symptoms show up even dizziness, and hallucinations occur. The gastrointestinal system though there are sufficient quantities in the diet, and the is also involved, and diarrhea, along with abdominal discom- vitamin must be received by injection. fort, nausea, and vomiting, is common. Another characteristic The most common result of B12 deficiency is pernicious of the condition is a bright red, or strawberry, tongue. anemia, characterized by the production of improperly formed Pellagra is especially common in areas where corn is red blood cells. The associated symptoms include fatigue and the dietary staple. Outbreaks have occurred in southern weakness because the delivery of oxygen to the body’s tissues Europe, particularly Italy, parts of southern India, and the is impaired. A more serious consequence of B12 deficiency is rural South in the United States, where the disease was epi- nerve damage that begins as a creeping numbness of the lower demic early in the twentieth century. It was estimated that extremities. 10,000 people died and another 200,000 were afflicted each In general, vitamin B12 is involved in nucleic acid syn- year. During this period, about half the patients in mental thesis and interacts with folic acid (another B vitamin) in this hospitals in the South were suffering from the dementia function. Because blood cells are constantly being formed in caused by pellagra. the bone marrow, this site of rapid cell division is one of the Although corn does contain some niacin, it is in a form first affected by impaired synthesis of DNA due to a deficiency that makes it unavailable; furthermore, corn is also deficient of either vitamin. These vitamins are, therefore, involved in the in tryptophan. However, pellagra was not a problem in the normal development of red blood cells, and a deficiency of traditional diet of the natives of Mexico, Central America, either vitamin causes anemia. The anemia can be treated with and parts of South America for two reasons. Lime (calcium either B12 or folic acid supplements. However, folic acid sup- oxide from wood ash or shells), used in the preparation of plements have no effect on the nerve damage caused by a B12 corn meal, is able to release the bound niacin. In addition, the deficiency, and the administration of folic acid for the anemia beans, squash, tomatoes, and peppers commonly eaten with can mask a true B12 deficiency and result in permanent neu- the corn also supplied niacin. rological degeneration. In this regard, vitamin B12 functions The addition of milk and meat to the diet was recom- in maintaining the sheath surrounding nerve fibers, which is mended to prevent pellagra long before the vitamin was identi- necessary for the transmission of nerve impulses. fied. Although meat contains niacin, milk is low in the vitamin Under directions from the FDA and the Department of but does supply tryptophan. Sources rich in niacin include Health and Human Services, U.S. manufacturers fortify most meat, poultry, fish, eggs, nuts, seeds, and legumes. One way enriched breads, flours, corn meals, rice, and other grain prod- the pellagra in the South could have been prevented was by the ucts with folic acid. This action was taken because it was deter- consumption of a handful of peanuts every other day, because mined that insufficient levels of folic acid contribute to spina peanuts are an excellent source of niacin. bifida (the backbone does not form properly, leaving the spinal There has been an increased interest in the therapeu- cord exposed) and other neural tube birth defects. Because tic value of megadoses of niacin (the nicotinic acid form) more than half of all pregnancies are unplanned and these for reducing blood cholesterol levels. Unfortunately, the defects of the spine and brain occur in the developing fetus megadoses can cause some toxicity symptoms, the most before most women realize they are pregnant, it is important common of which is a niacin flush. It produces a temporary that all women of childbearing age consume 0.4 milligram of warm flush of the skin, with a tingling or stinging sensation. folic acid daily. Since 1998, when folic acid fortification of Intestinal irritation and liver damage have also been reported. foods began, the number of neural tube birth defects in the The other form, nicotinamide, does not produce those tox- United States has dropped by one-third. icity symptoms but is not at all effective in lowering blood Adequate levels of folic acid may also afford protection cholesterol levels. from early heart disease. In patients with atherosclerosis,

Vitamin B12 Vitamin B12 (cobalamin) is unique in that it does not occur naturally in any foods of plant origin but occurs only in animal sources, where it is widely available. Those who completely eliminate meat, dairy products, and Thinking Critically Vitamins are classified according to their solubility. The eggs from their diets are at risk of developing a B12 deficiency unless they take vitamin supplements or eat fortified foods. water-soluble vitamins include C and the B complex. A, D, E, Soy milk, breakfast cereals, and meat substitutes are often and K are the fat-soluble vitamins. fortified with B12. Many people subscribe to the notion of vitamin The absorption of vitamin B12 in the small intestine megadosing to ensure better health and consume many requires the presence of a substance secreted by the stomach times the RDI for particular vitamins. What are the called an intrinsic factor. Poor absorption of B12 has been practical effects of vitamin solubility on this practice? reported in people who, because of a genetic defect, do not produce the intrinsic factor. This defect most often shows up

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high levels of plasma homocysteine are commonly found. Animal studies have shown that if bromine, active in the body Homocysteine is an intermediate in amino acid metabolism. It in the form of the bromide ion, is eliminated from the diet, is toxic to the lining of blood vessels, bringing about changes abnormal basement membranes form. Basement membranes that lead to cardiovascular disease. It may also promote are extracellular structures found in connective tissue which clotting factors in the blood. Normally, homocysteine is not form scaffolds that support tissues. Bromide ion is a necessary found in high levels in the bloodstream because it is broken cofactor for the enzyme peroxidasin; this enzyme catalyzes the down by enzymatic activity. Certain vitamins—folic acid is formation of sulfilimine (sulfur-nitrogen) bonds between pro- one—are cofactors for these enzymes. Many patients with tein ropes of collagen that make up the basement membrane. early coronary artery disease have low levels of folic acid and This research is of tremendous interest because it had been correspondingly high levels of homocysteine. Increasing the shown previously that cells in contact with abnormal base- nutritional intake of folic acid will decrease homocysteine ment membranes can become cancerous. Also it is known that levels as well as the risk of heart attack or stroke. thiocyanate, one of the chemicals in tobacco smoke, inhibits the enzyme peroxidasin, which leads to the breakdown of Minerals basement membranes in the lungs of smokers. Minerals are subdivided into two categories, the major Minerals are inorganic compounds that exist in the body as minerals, needed in amounts greater than 100 milligrams per ions (charged atoms) or as part of complex molecules. At day, and the trace minerals, needed in amounts no more than least 18 minerals are required for normal metabolic activi- a few milligrams per day. The following discussion will be lim- ties (table 10.7). In 2014, bromine was identified as another ited to calcium, a major mineral whose RDI has been recently essential element necessary for proper human nutrition. revised, and two trace minerals that have been extensively studied, iron and iodine.

Table 10.7 Calcium Dietary Mineral Requirements Calcium is the most abundant mineral in the body, with the average adult containing 800 to 1,300 grams of the element. Mineral Function Ninety-nine percent of the body’s calcium is found in the bones and teeth; the other 1% is in the blood and tissues. Major Minerals The concentration of calcium is under the control of several Calcium Bone and tooth formation, blood hormones and vitamin D. If the amount in the blood gets too clotting, nerve impulse transmission, low, calcium reserves in the bone are drawn upon to restore muscle contraction levels to the normal range. If the amount of calcium in the Phosphorus Nucleic acids, bone and tooth formation, blood is too high, more calcium is deposited in the bone cell membranes, ATP formation and more is excreted by the kidneys. Excess calcium intakes Sulfur Protein formation (12,000 milligrams per day and above are considered toxic) Potassium Muscle contraction, nerve impulse have been associated with increased risk of kidney stone for- transmission, electrolyte balance mation. In addition to forming the matrix of bones and teeth, Chlorine Gastric juice calcium in the body fluids is involved in many important func- Sodium Nerve impulse transmission, body tions: nerve impulse transmission, muscle action (including water balance heartbeat), blood clotting, cell membrane integrity, intracellu- Magnesium Protein formation, enzyme cofactor lar communication, and as a cofactor for enzymes (cofactors are mineral ions and, like coenzymes, are necessary for the Trace Minerals proper functioning of certain enzymes). Iron Hemoglobin Calcium deficiency may lead to osteoporosis, a degener- Zinc Component of many enzymes and ative bone disease that may strike older individuals without insulin, wound healing warning. In osteoporosis, the bone density is greatly reduced Iodine Component of thyroid hormones (osteoporosis literally means porous bone), resulting in bones Fluorine Bone and tooth formation that fracture readily. This condition can result from years of Copper Enzyme component, red blood cell low dietary calcium intake or poor absorption of calcium from formation the intestines (caused by lack of vitamin D or other factors). Selenium Antioxidant To maintain blood calcium levels, the reserves in the bone are

Cobalt Component of vitamin B12 dangerously depleted. Postmenopausal women are particularly Chromium Normal glucose metabolism at risk of developing osteoporosis because bone loss is accel- Manganese Enzyme cofactor erated at this time. Estrogen replacement therapy appears to Molybdenum Enzyme cofactor retard this bone loss, but is associated with a higher risk of Bromine Enzyme cofactor breast cancer, heart attacks, and strokes. Adequate dietary cal- cium and regular exercise also prevent osteoporosis; however,

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there are many interacting factors (both genetic and environ- inland areas, especially mountainous regions, are likely to mental), and much more research is needed in this area. have iodine-deficient soils. It is in these areas where people Milk and milk products are among the best sources of may develop the iodine-deficiency disease endemic, or simple, calcium, but the element is also present in dark green leafy veg- goiter. In the United States, the area around the Great Lakes etables, many seeds, and other foods. Unfortunately, in some was formerly known as the “goiter belt” because of the high vegetables, the presence of oxalic acid inhibits the absorption incidence of goiter. The most obvious symptom of goiter is a of calcium. Recently, the RDI for dietary calcium for adults swelling of the neck caused by an enlargement of the thyroid over 50 has been increased to 1,200 milligrams to prevent the gland, which straddles the trachea. development of osteoporosis. New evidence has also shown Iodine is required for the formation of thyroid hormones, that calcium, together with vitamin D, may provide protection which regulate metabolism in all cells of the body and control against colon cancer; the amount of calcium required for this body temperature, growth, development, and reproduction. beneficial action is 1,500 milligrams per day. When the amount of iodine is low, hormone production is impaired. The thyroid enlarges in an attempt to produce more Iron of the needed hormones; this attempt is futile without the nec- Although most of the trace minerals are usually found in ade- essary iodine. A person suffering from simple goiter exhibits quate amounts in a well-balanced diet, iron and iodine present a lack of energy, decreased blood pressure, sensitivity to cold special problems. Iron deficiency is common in women and temperatures, and weight gain. children, and care must be taken to ensure that the diet supplies Goiter has been a recognized ailment since ancient times, sufficient quantities of the element. Meat, especially liver and and various treatments have been suggested as a cure. The other organ meats, shellfish, fish, and poultry are excellent iron earliest known treatment is recorded in a Chinese source from sources. Many foods from plants are also rich in iron, including 5,000 years ago that recommended eating seaweed and burned dark green leafy vegetables, dried fruits, legumes, whole grains, marine sponge. Today it is known, of course, that organisms and enriched breads and cereal products. Overall, only about from the ocean are naturally rich in iodine. The relationship 10% of dietary iron is actually absorbed by the body, with the between iodine and goiter was confirmed in 1820 by the absorption dependent on the type of iron compound present; French physician Jean-Francois Coindet, who reported the the rest is eliminated in the feces. The iron from animal sources treatment of goiter using doses of iodine salts. Today goiter is may be present as heme iron (40%) or nonheme iron (60%), rare in the United States and Europe because of iodized table whereas the iron in plant sources is nonheme. Heme iron salt, first introduced in 1924. However, in other areas of the is more readily absorbed by the body, but the absorption of world, almost 200 million people still suffer from goiter, an nonheme iron can be improved by the presence of vitamin C. easily preventable disorder. The most important role of iron is as a component of More than half of the salt sold in the United States is hemoglobin, the molecule that carries oxygen in red blood iodized, and a single teaspoon of this salt supplies almost cells; in fact, it is the iron that imparts the red color to these twice the RDI of 0.15 milligram. However, overconsumption cells. In addition, iron occurs in myoglobin, a molecule similar of iodine-containing substances can also be a problem because to hemoglobin, the oxygen carrier in muscle cells; in several iodine can be toxic. As little as 2.0 milligrams per day is consid- storage proteins in the liver, bone marrow, and spleen; and in ered toxic, resulting also in an enlargement of the thyroid gland. enzymes present in each cell. In addition to a lack (or even an excess) of dietary iodine, Because the majority of iron is found in hemoglobin, iron goiter can result from the overconsumption of goitrogenic deficiency has its greatest impact on red blood cells. When compounds. Certain medications, including some of the sulfa iron reserves in the body are low, not enough hemoglobin drugs, and vegetables in the cabbage family are known to con- can be synthesized for newly formed red blood cells. These tain compounds that block the utilization of iodine in the thy- cells are smaller, paler, and less efficient in oxygen transport roid. In a varied diet, these compounds are harmless, but they than are normal red blood cells and are characteristic of may be a problem in diets restricted solely to those vegetables. iron-deficiency anemia, the most common dietary deficiency disease in the world. The symptoms of iron-deficiency anemia include fatigue, inability to concentrate, pale coloration, weak- ness, and listlessness. Thinking Critically The greatest risk of iron toxicity comes from overdosing The macronutrients (carbohydrates, proteins, and fats) are on iron supplements, which can result in damage to the liver required in relatively large amounts for proper nutrition, and pancreas and even sudden death in young children. whereas the micronutrients, the vitamins and minerals, are needed in smaller quantities. Iodine Since micronutrients are required in much smaller The presence of iodine in food is dependent on the availability amounts than macronutrients, are they any less important of iodine in the natural environment where the plant or ani- to the human diet? Explain. mal developed. Foods from the ocean are reliable sources of iodine because this element is plentiful in seawater. In general,

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intake, proteins about 8%–10%, and fats no more than 30%, DIETARY GUIDELINES with 10% each from saturated, monounsaturated, and poly- unsaturated fat sources. Since the first dietary guidelines Research has shown that many significant diseases are influ- were issued, some healthy trends have developed among the enced by nutrition, and beneficial changes in diet can, there- American people. Fresh fruits, vegetables, and whole-grain fore, reduce the risk of developing these conditions. Diseases products have undergone a resurgence in popularity, owing linked to nutrition are some of the major causes of death to expanded selections available in the supermarkets and in the United States: cardiovascular diseases, hypertension, increased nutritional awareness of the value of fiber. some forms of cancer, and type 2 diabetes. These diseases Although the guidelines call for a reduction in the con- may arise in part from excess consumption of fat (especially sumption of refined and processed sugars, consumption has saturated fat), cholesterol, refined sugar, and salt. In light of continued to rise (a trend that began early in the twentieth cen- these findings, government agencies and health professionals tury). At least part of the rise is attributable to the increased have recommended dietary guidelines for better health and the consumption of soft drinks, which contain high-fructose corn prevention of disease. syrup. Americans are eating less red meat, eggs, and whole dairy Balancing Nutritional Requirements products than ever before, which is a good trend for reduc- The U.S. Senate Select Committee on Nutrition and Human ing saturated fats and cholesterol. Consumption of poultry Needs issued the first Dietary Goals for the United States and fish has increased as consumption of beef has declined, in 1977. This was followed in 1980 by the publication of and low-fat dairy products have become the preferred choice Nutrition and Your Health: Dietary Guidelines for Americans, for many people. Although the intake of saturated fat has issued jointly by the U.S. Department of Health and Human decreased (dramatically for butter and lard), more plant oils Services (HHS) and the U.S. Department of Agriculture are being consumed. This trend has had a significant agricul- (USDA). Revisions of the Dietary Guidelines have fol- tural impact, as farmers have increased the acreage devoted lowed every 5 years. The latest revision of the USDA rec- to growing oil crops, such as sunflower, safflower, rapeseed ommendations, Dietary Guidelines for Americans, 2010, featured MyPlate (fig. 10.5), which replaced the Food Pyramid. Some of its recommendations are as follows: 1. Make half your plate fruits and vegeta- bles; especially red, orange, and dark green-vegetables. Eat fruit, vegetables, and unsalted nuts as snacks. 2. Drink fat-free or low-fat (1%) milk. Try calcium-fortified soy products as a sub- stitute for dairy foods. 3. Make at least half of your grains whole by choosing whole-grain cereals, breads, and pasta. 4. Vary protein choices by eating seafood twice a week and eating beans. Eat smaller and lean portions of meat and poultry. 5. Cut back on foods and drinks high in saturated fats, added sugars, and salt. Replace sugary drinks such as soda with water. Choose low-sodium ver- sions of soups, bread, and frozen meals. 6. Balance Calories by eating less and avoiding oversized portions. Be physi- CDC cally active. Figure 10.5 MyPlate illustrates the 2010 Dietary Guidelines for Americans, which The dietary guidelines originally sug- offer the best scientific advice on how to eat for health issued by the USDA. gested that complex carbohydrates should Source: http://www.choosemyplate.gov/food-groups/downloads/MyPlate/MyPlateGraphicsStandards.pdf. make up about 60% of the daily caloric Source: USDA

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(canola oil), corn, and soybean. Margarine, shortening, salad complex carbohydrates, such as breads, cereals, rice, and oils, and cooking oils account for the expanded use of plant pasta, to 60% of the daily diet. Other directives were to limit oils, but remember, if the plant oils are hydrogenated, they dairy products and protein sources (meat, eggs, fish, poultry, have reduced health value. and beans) to two to three servings for each group per day Since the early 1980s, there has been a heightened and increase the number of servings of fruits and vegetables awareness about the dangers of high blood cholesterol levels, eaten daily. and Americans have responded with changes in diet and exer- The most controversial aspect of previous Dietary cise. A report on several thousand men and women showed Guidelines is the advice about fats and carbohydrates. Many a decrease in cholesterol levels: for men, the 1980–1982 researchers are coming to the conclusion that it is just too sim- average was 205 milligrams, lowered to 200 milligrams in plistic to advocate eating all types of complex carbohydrates the 1985–1987 study; likewise, women showed a drop from and avoid all types of fats. Increasingly, it has been shown that 201 milligrams to 195 milligrams in the same period. This there is no nutritional evidence that a diet high in complex trend indicates that many Americans are attempting to keep carbohydrates and low in all fats is beneficial to health. In fact, blood cholesterol at or below the recommended level of the reverse may be true. 200 milligrams. Although it is known that a diet high in saturated fats Although sodium is one of the major minerals, most raises total blood cholesterol levels and that high cholesterol Americans ingest more sodium (in the form of sodium is associated with an increased risk of coronary heart disease, chloride—table salt) than required; high sodium intake is certain fats, as stated previously, are beneficial to health. related to hypertension (high blood pressure). Excessive salt Monounsaturated fats, such as olive oil, can reduce the risk of ions in the bloodstream draw water from the tissues, thereby cardiovascular disease by lowering LDL cholesterol levels and raising the fluid pressure in the blood vessels. A low-salt raising HDL cholesterol. It has also been shown that a diet of diet may be effective in lowering blood pressure in sodium-- polyunsaturated fats can reduce total blood cholesterol levels. sensitive individuals. Some foods naturally contain sodium, For example, the so-called Mediterranean diet common but much of the sodium in our diet comes from the table salt in Italy, France, and Greece, in which fats make up 40% of the added during cooking, during the meal, or in prepared foods. total kilocalories, is associated with a low rate of heart disease. In fact, two-thirds of dietary salt is actually “hidden” in com- Apparently, the type of fats—mainly monounsaturated olive oil mercially prepared food and beverages. and polyunsaturated fish oils with omega-3 fatty acids—not the percentage, is the determining factor in lowering the incidence of heart disease. Healthier Dietary Guidelines The original intent of the earlier USDA Dietary Guidelines In February 2004, the CDC (Centers for Disease Control and was to influence the American public to decrease consumption Prevention) released the results of a study on the prevalence of saturated fats. At the time, it was thought to be too difficult of obesity and the changes to the American diet over the past for the public to distinguish saturated fats from other types of 30 years. The incidence of obese individuals in the total U.S. fats, so the message was simplified to decrease consumption adult population increased from 14.5% in 1971 to nearly 31% of all fats to 30% of total kilocalories, down from the 40% typ- in 2000 as the average amount of kilocalories per day rose. ical of the American diet. To compensate for the kilocalories For men, the average energy intake increased from 2,450 lost by decreased fat consumption, the percentage of complex in 1971 to 2,618. The rise in energy intake for women was carbohydrates was raised from 45% to 60%. The recommended nearly double that at 335 kilocalories. As Americans ate more daily percentage of protein stayed about the same at 10%–15% and got fatter, what they ate changed, too. Carbohydrates because there was concern that, if increased protein consump- made up a greater percentage of the American diet. For men, tion was recommended, people would eat more red meat as a carbohydrate intake increased from about 42% to 49%; for protein source without realizing that red meat is usually asso- women, carbohydrates rose from approximately 45% to 52% of ciated with saturated fat. “Fats are bad” was the rallying cry of the daily diet. At the same time, the percentage of both total the earlier Dietary Guidelines. fat and saturated fat in the diet declined. For men, total fat Unfortunately, this message was the wrong one. Nutritional decreased from 37% to 33%, and saturated fat fell from 14% studies from the early 1990s have shown that, if people replace to 11%; for women, total fat and saturated fat fell from 36% kilocalories from saturated fat with an equal amount from car- to 33% and 13% to 11%, respectively. Protein levels for both bohydrates, their LDL and total cholesterol levels do fall, but men and women declined slightly from an average of approx- so does their level of HDL. Similarly, if people eat a diet high imately 17% to just over 15%. As many low-carbohydrate in monounsaturated or polyunsaturated fats but then switch to dieters suggest, the rise in obesity in the United States appears an equivalent amount of kilocalories from carbohydrates, their to be correlated with a rise in carbohydrates, especially refined LDL levels rise and HDL levels decline. starches and sugars. Trans fatty acids found in many dietary substitutes for This trend is especially disheartening because earlier ver- foods rich in saturated fats are uniquely bad because they sions of the USDA Dietary Guidelines advised Americans to raise LDL and triglycerides while reducing HDL. Eating trans minimize consumption of fats to just 30% per day and increase fatty acids greatly increases the risk of cardiovascular disease.

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In contrast, consuming saturated fats increases the risk only A high GI diet is associated with a greater risk of heart slightly because consumption of saturated fats increases LDL disease, type 2 diabetes, and obesity. A diet high in GI car- but also HDL. bohydrates raises blood triglyceride levels and lowers HDL Another common misconception is that eating a greater cholesterol, increasing the risk of coronary heart disease. percentage of fats in the daily diet is linked to obesity because Another consequence of a high GI diet is insulin resistance, fats have more than double the kilocalories of equal portions common in many overweight, sedentary people. One of the of proteins or carbohydrates. The standard advice has been to main indicators of insulin resistance, also known as Syndrome avoid obesity by eating a low-fat diet. The only way to avoid X, is a sustained high blood glucose level after the ingestion obesity is to lower total kilocalories, not just fat kilocalories, of high GI foods. Although insulin is produced in affected and increase energy expenditure through physical activity. individuals, it is not as effective in moving glucose from the No nutritional studies have definitively linked the con- bloodstream into body cells. Because the insulin is not as sumption of fat with a higher risk of breast or colon cancer. effective, more and more insulin is released to do the job of A diet high in red meat has been associated with a higher risk moving glucose out of the blood and into cells. Eventually, of colon cancer, but this link is probably due to carcinogens the insulin-producing cells of the pancreas become overtaxed produced during cooking and the type of chemicals found in by higher production levels and give out. People who exhibit processed meat. A low-fat diet has not been shown to reduce insulin resistance have a higher risk of hypertension, heart the risk of cancer. A 2006 study on women’s health compared disease, and most significantly type 2 diabetes. Foods with the women who reduced fat consumption from 8% to 10% over a highest GI numbers correspond with greater insulin release, period of 8 years with a control group. In that study, the rates and the higher the insulin spike, the lower the blood glucose for colon and heart disease were not statistically different, but sinks. Low blood glucose stimulates hunger and a craving for the rate of breast cancer showed a small decline. more high GI foods, which may lead to overeating and weight Incorporating weight control and physical activity appear gain. In contrast, low GI foods are digested more slowly, glu- to be the key factors in decreasing the risk of many cancers. cose levels in the blood drop gradually, and it takes longer for Unfortunately, recent data did find that sedentary, overweight hunger to return. women who ate diets high in refined carbohydrates had a high Another problem with the previous USDA Dietary incidence of both pancreatic and breast cancer. Increasingly, Guidelines was that they did not distinguish between dif- evidence points out that a diet high in certain carbohydrates is ferent sources of protein. They lumped red meat, poultry, not synonymous with healthy eating. fish, legumes, nuts, and eggs into a single group, despite the evidence that a diet high in red meat is high in saturated fats and cholesterol and is associated with an increased risk Glycemic Index of coronary heart disease and type 2 diabetes. Poultry and Some carbohydrates are readily digested and quickly metab- fish possess fewer saturated fats, and fish are a source of olized by the body into glucose. A rapid increase in blood beneficial omega-3 fatty acids. Certain nuts, such as walnuts, glucose stimulates the release of insulin from the pancreas. are also rich in beneficial omega-3 fatty acids but regrettably Insulin facilitates the uptake of glucose into body cells, such high in Calories. What’s more, the pyramid promoted over- as muscle and fat cells, and quickly lowers blood sugar levels. consumption of dairy products, a recommendation that was Glycemic index (GI) measures the effect that a particular food initially made to ensure significant calcium content in the has on blood glucose levels. The faster the food is converted diet to prevent osteoporosis. The problem is that most dairy to glucose, the higher the GI number. White bread, white rice, products are associated with saturated fat and high caloric and white potatoes are examples of carbohydrates with rela- values. The best advice for those concerned about obtaining tively high GI values. Whole grains, and high-fiber fruits and sufficient calcium for preventing osteoporosis would be to vegetables have lower GI ratings. A more practical measure take calcium supplements. The Dietary Guidelines do advo- that is often used is glycemic load, which takes the GI value for cate eating plenty of fruits and vegetables, but consumption a food and multiplies it by the number of carbohydrate grams of the white potato and other starchy vegetables should be the food contains. Thus, many fruits and vegetables that have limited. a relatively high GI value have a much lower glycemic load. An improved version of the Dietary Guidelines, as sug- Fiber slows the rate of digestion, and high-carbohydrate foods, gested by Walter Willett of the Harvard School of Public such as many beans, that also are high in fiber have a lower GI. Health, emphasizes keeping one’s weight under control There are difficulties in accurately determining the GI for through daily exercising and avoiding an excessive total intake a particular food because the calculation is based on the aver- of kilocalories. It recommends that the majority of one’s daily age blood glucose response of 10 subjects after they have eaten diet should be the consumption of the healthy monounsat- a particular food. Different people have different responses urated and polyunsaturated fats and healthy carbohydrates, to the same food, and the same person may have a different whole-grain and unrefined. A variety of fruits and nonstarchy response on a different day. Eating different combinations of vegetables with protective phytochemicals should be eaten in foods and changing the method of cooking can also alter the abundance. Healthy protein sources, such as nuts, legumes, GI value. fish, poultry, and eggs, should be eaten in moderation. Dairy

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Cancer has been a dreaded disease for centuries, and it con- beverages enhances the risk of cancers of the upper respi- tinues to plague humanity today. The term cancer actually ratory tract, digestive tract, and liver. Eating heavily salted refers to over 100 forms of a disease that can strike just foods and drinking extremely hot beverages have been about every tissue and organ in the body that shares several linked to cancers of the stomach and esophagus, respec- basic processes. Cancer cells are abnormal cells that prolif- tively, in countries outside the United States where these erate uncontrollably, forming masses called tumors. Cancer dietary habits are customary. cells also possess the ability to migrate, or metastasize, from Ironically, the latest research suggests that what is miss- the original site, forming tumors in other parts of the body. ing in our diets may be far more important in causing can- It is the interference of malignant tumors with normal body cer than what we actually eat or drink. Components called functioning that makes cancer lethal. phytochemicals, which occur naturally in vegetables, fruits, A number of agents have been identified as carcinogens grains, and seeds, have been investigated for their protec- (cancer-causing agents)—certain microbes, ultraviolet radia- tive action in the prevention of cancer and other diseases. tion, chemicals (such as PCBs, arsenic, and benzene), radon, Cruciferous vegetables (broccoli, cauliflower, cabbage, and and various gene mutations—but more than half of all can- so on) are excellent sources of one class of chemopreventive cers in the United States are related to tobacco smoke and chemicals: the dithiolthiones. In laboratory animals treated diet. In addition to tars, a number of known carcinogens are with a synthetic version of one of the dithiolthiones, tumors of found in tobacco smoke (see Chapter 20). Not surprisingly, the lung, colon, mammary glands, and bladder were inhibited. smoking—especially cigarette smoking—is associated with One of the most potent dithiolthiones is sulforaphane, found several cancers: lung, upper respiratory tract, esophageal, in broccoli, which has been shown to inhibit breast cancer in bladder, and pancreatic. Tobacco smoke is also implicated in rats. Both of these phytochemicals apparently work by acti- stomach, liver, kidney, and pancreas cancers and in leukemia. vating liver enzymes that destroy carcinogens in the body. Diet is second only to smoking as a major cause of can- Genistein, a compound found in soy products (derived cer in the United States. Red meat has been identified as from the soybean), prevents the formation of breast tumors an associative cause of colon, rectal, and prostate cancers. in rats in a different manner. It inhibits the formation and Obesity in adults is linked to cancers of the uterus, breast, growth of blood vessels to a growing tumor. Without these colon, kidney, and gallbladder. Abusive drinking of alcoholic sources of nutrients and oxygen, the tumor cannot grow.

products should be limited to one or two servings daily. The vegetarianism: lacto vegetarians, lacto-ovo vegetarians, and consumption of red meat, saturated fats, refined grains, and vegans. Some vegetarians, such as the lacto and the lacto-ovo, starchy fruits and vegetables should be restricted. Trans fatty consume dairy products or dairy products and eggs but do not acids should be avoided completely. A daily multiple vitamin consume animal flesh. Vegans are pure vegetarians, consum- and mineral supplement should be taken. Alcohol consump- ing no animal products at all. Some other vegetarians stretch tion of beer, wine, or distilled spirits in moderation is accept- the concept by consuming fish and poultry, avoiding only red able because of evidence of its benefit to the cardiovascular meat. system (see Chapter 24). There are several health benefits to increasing the con- Recently, Willett conducted a study on the health of men sumption of plant products while decreasing the consump- and women who followed his dietary suggestions. He found tion of animal products. Vegetarians are less likely to suffer that they had reduced the risk of cardiovascular disease by 30% from the chronic diseases that afflict many Americans whose for women and 40% for men. These findings and others have diets are high in animal products. Blood cholesterol and resulted in major revisions within the USDA Dietary Guidelines, triglyceride levels usually reflect the amount of animal fat in 2010 and illustrated in the release of MyPlate. the diet and are lowest in vegans, who, consequently, have a lower incidence of heart disease. Those cancers linked to red meat and dairy consumption (colon and prostate) are less Meatless Alternatives common in vegetarians. High fiber in a vegetarian diet also With the awareness about the dangers of saturated fat and plays a role in reducing risks of type 2 diabetes and lowering cholesterol inherent in animal products, many Americans cholesterol levels. (See A Closer Look 10.2: Eat Broccoli are incorporating a greater percentage of vegetables, fruits, for Cancer Prevention.) A further benefit of high-fiber diets grains, and legumes into their diets. Some even choose a is in weight control; the filling effect of fiber suppresses totally vegetarian lifestyle. There are many different forms of overeating. 172

lev80044_ch10_152-174.indd 172 2/19/19 11:54 AM Studying populations that drink quantities of green tea Matters™ which calculates the servings of fruits and vege- (made from unfermented tea leaves, Chapter 16) has revealed tables on the basis of age, gender and activity level. Several a lower incidence of many cancers, especially those of the studies appear to support this belief. Beta-carotene, the breast and prostate. Green tea contains a high percentage yellow-orange pigment associated most commonly with car- of chemical agents (flavonoids) known as catechins, and in rots, was given to people at risk of developing lung cancer particular, epigallocatechin gallate. For a cancer to metas- as a supplement in a chemoprevention trial sponsored by tasize, certain enzymes are needed. One of these crucial the National Cancer Institute. Surprisingly, the group given enzymes is urokinase, and it appears that catechins inhibit beta-carotene had a slightly higher rate of lung cancer it and thus prevent the invasion and spread of cancer cells than the group given a placebo. A 2007 review of nearly to distant sites. In the processing of black tea, the type of 70 studies also found that adults who take supplements of tea most commonly drunk by Americans, epigallocatechin beta- carotene, vitamin A, and/or vitamin E had higher mor- gallate is destroyed and thus does not afford the same pro- tality rates than those who did not or who were given a pla- tective benefits associated with the drinking of green tea. cebo. Adults who took supplements of vitamin C or selenium In 2010, it was shown that epigallocatechin gallate (EGCG) showed no difference in death rates than the control group. can interfere with certain anticancer drugs, such as borte- Recent large, long-term studies looking at a diet high in zomib. Bortezomib is given to patients who are suffering fruits and vegetables to reduce the risk of breast cancer from multiple myeloma, an incurable but treatable form of have failed to substantiate the promise of earlier laboratory cancer of blood cells in the bone marrow. Bortezomib acts work. Those who consumed the greatest amount of fruits by deactivating proteasomes (see Chapter 2); however, in the and vegetables did, however, show a 25% reduction in the presence of EGCG, its anticancer activity is inhibited. It was risk of cardiovascular disease. Critics point out flaws in observed, however, that only proteasome deactivators that questionnaires and the difficulties that participants have in contain boron, as does bortezomib, are inhibited by EGCG. accurately recording and quantifying their diets. Also, some Green tea does not interfere with the proteasome inhibition suggest that the protective effect may be conferred during of other anticancer drugs that lack boron. Patients undergo- a critical period in childhood, but no study has examined the ing treatment with bortezomib should refrain from drinking connection between a girl’s diet and breast cancer. Another green tea or taking supplements of green tea extracts. study found that women who had the highest blood con- Phytochemicals appear to be most effective if eaten in centration of carotenoids, such as beta-carotene, showed foods rich in these cancer-preventive agents rather than the lowest incidence of breast cancer. But the same study administered as supplements. In fact, the National Cancer showed no difference in the incidence of breast cancer with Institute initiated the 5-A-Day Program in 1991 to encourage the amount of vegetables and fruits consumed, suggesting the public to eat five or more servings of vegetables and that individual differences in metabolism to harvest pro- fruits every day. In 2007, the CDC and the Produce for Better tective phytochemicals may be more important. The work Health Foundation (PBH) released Fruits and Veggies—More continues.

Vegetarians, especially vegans, must be knowledgeable 2. Carbohydrates include simple sugars, such as the mono- about all the nutritional requirements and use care in selecting saccharides fructose and glucose and the disaccharides plant sources that meet those requirements. Special attention sucrose and lactose. Complex carbohydrates, or polysac- must be given to ensure that iron, the B vitamins (especially charides, include starch and glycogen and act as the body’s B12), calcium, vitamin D, and the essential amino acids are fuel. Dietary fiber includes both soluble and insoluble forms supplied. Complementing the essential amino acids is of prime that provide beneficial health effects, acting as roughage, importance because all plant proteins are incomplete. This can promoting regularity, and lowering blood cholesterol levels. be easily accomplished by eating legumes and grains that, in 3. All plant proteins are incomplete, deficient in one or more combination, provide an excellent source of protein for the diet. essential amino acids. But complementing incomplete In fact, one study indicates that proteins from plant foods may be plant proteins, such as combining legumes and cereals in a preferable to animal protein because consumption of excessive single meal, can overcome this deficiency. Gluten in wheat animal protein itself, not just animal fat, may be linked to heart can trigger celiac disease in individuals who have an inher- disease and cancer. The suggestion is that meat should no longer ited sensitivity to this protein. be the centerpiece of a meal but instead relegated to a side dish 4. Lipids include fats and oils, and most of the dietary lipids for a vegetarian entrée. Perhaps vegetarians have the right idea. are classified as triglycerides. A diet high in saturated fats raises the risk of cardiovascular disease. Unsaturated fats, whether monounsaturated or polyunsaturated, lower the CHAPTER SUMMARY risk of cardiovascular disease by lowering LDL cholesterol 1. The nutritional needs of the human diet can be categorized levels. Foods of animal origin generally are high in satu- into the macronutrients (carbohydrates, proteins, lipids) rated fats and cholesterol, but foods of plant origin lack and micronutrients (vitamins and minerals). cholesterol and contain mainly unsaturated fats. 173

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5. Deficiency diseases result if a diet lacks any of the essential 3. What is the role of gluten in celiac disease? vitamins and minerals. Fat-soluble vitamins (A, D, E, and 4. What is the role of lipids in the body? What is the dietary K) can be stored by the body but can build up to toxic levels significance of saturated and unsaturated fats? if excessive amounts are taken. Water-soluble vitamins (C 5. Describe the following deficiency diseases: scurvy, rickets, and B complex) cannot be stored in appreciable quantities marasmus, beriberi, osteoporosis. by the body. Most vitamins and minerals (the exception 6. How closely do you follow the recommended dietary is vitamin B12) can be found in foods of plant origin. The category of minerals (major or trace) is defined by the guidelines? Evaluate your diet in terms of a healthy lifestyle. quantity needed in the body. 7. What are the dietary causes of anemia? 6. Americans should modify their diets for a healthier life- 8. What differentiates simple carbohydrates from complex style. Some fats, such as monounsaturated and polyunsat- carbohydrates? urated fats, are heart-healthy and should become a regular 9. What dietary factors influence the development of cardio- part of the diet. Saturated fats, however, should be limited vascular diseases or cancer? and trans fats avoided completely. Limit the consumption 10. Estimate the amount of protein you consume in a typical of white bread, white rice, white potato, and other high day. What portion is from animal food sources, and what glycemic index carbohydrates to reduce the risk of type 2 portion is from plant foods? diabetes. Limit dairy products that are high in kilocalories and saturated fat. Eat plenty of nonstarchy fruits and veg- 11. Your friend insists that a vegetarian diet is unhealthy etables, and take a daily vitamin and mineral supplement. because proteins found in plants are never complete. How The most important factor for a healthier life is to keep would you respond? weight under control by limiting total caloric consumption 12. Concerned about your risk of cardiovascular disease, you and exercising regularly. undergo a blood test for cholesterol at a health fair at the local supermarket. The test results indicate your total cholesterol count is 190. Is further testing necessary? REVIEW QUESTIONS 1. If fiber is largely indigestible, why is it required for a healthy diet? 2. What are the essential amino acids? Why is it important that they be consumed?

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